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Setting a default value if a variable is empty

This is the pattern I've been using for "if the variable is empty, set a default value", and for variables like $muffin , it has all seemed well and good. But in the following real example, this pattern gives me a super long line which smells a bit to me. Is there a cleaner way to do this?

Jamal's user avatar

  • \$\begingroup\$ Starting with PHP 7.0, Langen's answer is probably the best: $newsItems[0]['image_url'] = $newsItems[0]['image_url'] ?? '/img/cat_placeholder.jpg'; php.net/manual/en/… \$\endgroup\$ –  oliverpool Commented Mar 24, 2017 at 10:08
  • \$\begingroup\$ Starting with PHP 7.4 there is a native operator - ??= \$\endgroup\$ –  SamGoody Commented Jun 25, 2020 at 23:04

7 Answers 7

reader from the future! PHP 7.0 introduced ?? which is a null coalescing operator, just use that: https://www.php.net/manual/en/migration70.new-features.php#migration70.new-features.null-coalesce-op .

Before dealing with your question, I'd like to point out that you probably want to use empty() instead of comparing with an empty string and that if you really want to compare to an empty string, use the === operator.

Anyway, default initialization is a real problem in many languages. C# even has a ?? operator to solve this kind of issue! So, let's try to make it better to make your code better step by step.

Ternary operator no more

The one-liner is too long, and using the ternary operator on multiple lines is a bad idea: that's what if-statement are for:

This is more readable for two reasons : it's easier to understand the syntax, but more importantly, it's easier to see that you simply want a default value when there's nothing. We don't need the 'else' part which is confusing with the ternary operator.

Note: as mentioned by Simon Scarfe and corrected by mseancole, PHP also has some special ternary syntax to do this:

Factorize it!

If you're doing this only once or twice, then all is good, but otherwise you'd want to factorize it into a function, since you don't repeat yourself, right? The simple way is:

(The ternary operator does make sense here since variable names are short and both branches of the condition are useful.)

However, we're looking up $newsItems[0]['image_url'] when calling default_value , and this is possibly not defined, and will raise an error/warning. If that's a concern (it should), stick to the first version, or look at this other answer that gives a more robust solution at the expense of storing PHP code as a a string and thus cannot be checked syntactically.

Still too long

If we don't care about the warning/error, can we do better? Yes we can! We're writing the variable name twice, but passing by reference can help us here:

It's much shorter, and feels more declarative: you can look at a bunch of default_value calls and see what the default values are instantly. But we still have the same warning/error issue.

Quentin Pradet's user avatar

  • 1 \$\begingroup\$ The second two options presented here will raise an error and also (because of this) impact performance. I shouldn't have to mention the performance bit, though, as the fact that an error (Warning, in this case, undefined index) should simply be enough. Even if reporting/logging is turned off, the fact that the interpreter notices at all incurs more performance impact than empty and isset in conjunction with an if . Stick to the if , or use a solution like mine below. \$\endgroup\$ –  Mike Commented Jan 6, 2015 at 21:39
  • \$\begingroup\$ Thank you, upvoted. Of course, the performance does not matter here, unless it is proven that this code is part of a bottleneck. \$\endgroup\$ –  Quentin Pradet Commented Jan 7, 2015 at 7:57
  • \$\begingroup\$ @MichaelJMulligan does my edit seem fair? \$\endgroup\$ –  Quentin Pradet Commented Jan 7, 2015 at 8:03
  • \$\begingroup\$ @QuentinPradet, Fair. As for the syntactic check, can you elaborate on my answer? I'd be interested. \$\endgroup\$ –  Mike Commented Jan 7, 2015 at 15:45

From here :

Since PHP 5.3, it is possible to leave out the middle part of the ternary operator. Expression expr1 ?: expr3 returns expr1 if expr1 evaluates to TRUE, and expr3 otherwise.

So could you write?:

Community's user avatar

  • 3 \$\begingroup\$ This is one of my favorite things to write in PHP. It feels elegant and naughty at the same time! :) I normally only use it when assigning to another variable or return from a function, though. \$\endgroup\$ –  David Harkness Commented Jul 15, 2012 at 2:06
  • 7 \$\begingroup\$ Note that if your variable is undefined, PHP will throw notices about it. This, unfortunately, is no replacement for $var = isset($var) ? $var : 'default value'; \$\endgroup\$ –  Brad Commented Jun 2, 2014 at 14:59
  • \$\begingroup\$ That's amazing, so clean and elegant :-) \$\endgroup\$ –  Avishai Commented Sep 28, 2016 at 20:23

Lo and behold, the power of PHP 7's null coalesce operator! It is also called the isset ternary operator, for obvious reasons.

Here's a passage from php.net's wiki page about it

Proposal The coalesce, or ??, operator is added, which returns the result of its first operand if it exists and is not NULL, or else its second operand. This means the $_GET['mykey'] ?? "" is completely safe and will not raise an E_NOTICE .

This is what it looks like

$survey_answers = $_POST['survey_questions'] ?? null;

It can even be chained. It'll use the first value that exists and isn't null, consider the following:

This would result in 11 , however if $a = null; it would print test .

Lando's user avatar

  • \$\begingroup\$ This is now integrated: php.net/manual/en/… \$\endgroup\$ –  oliverpool Commented Mar 24, 2017 at 10:05

The extract() function can also help.

It doesn't work for individual array keys like you have here, but it could be useful in other circumstances.

This will assign bar to $foo as a default value only if it's not already set. If $foo is already set it will skip it. You can include multiple variables in the array.

Ariel's user avatar

Doing it OOP style

If you are doing OOP you could also reconsider if using a plain array is the way to go. I guess image_url is not the only attribute of your news items, so convert this array structure to an object . Furthermore, $newsItems may get changed to an array of NewsItem instances.

/img/cat_placeholder.jpg could be the default value of the attribute image_url in your new class NewsItem. Either your client code decides whether to set a new value (e.g. based on being !empty() ) or your NewsItem class has a setter method for the attribute image_url ' that automatically sets the default value if it gets an empty string.

mdo's user avatar

PHP 7.4 adds ??= , the null coalescing assignment operator , which is exactly what you need.

This is functionally equivalent to the following, or to your examples:

SamGoody's user avatar

  • \$\begingroup\$ !isset() does not check if the value is falsey (like in the asker's script), only if the variable is undeclared or null . ??= does not check if the value is falsey, only if the variable is undeclared or is null . This answer is misleading/incorrect. \$\endgroup\$ –  mickmackusa Commented Oct 26, 2022 at 21:59

Do not do either of these two things:

Both will raise errors due to an undefined index (both first attempt getting the value at the index first) if the index is not set. This is a small thing, but even if you have error reporting AND logging turned off, the error is raised, is built, and propagates through the stack before it is checked if there is anywhere to report the error. And thus, simply doing something that CAN raise an error, incurs a performance hit.

Keep this in mind, because this goes for all Error Types (Notices, Warnings, etc), and in large apps can be a big deal. To avoid this you must use a function that does not raise an error on a missing index, like isset($array['index']) or empty($array['index']) , and not use the shortened ternary form.

Try a function like:

This doesn't raise errors, and will create the path if it does not exist. It also benefits from consolidating the logic to set defaults in one place, rather than if s everywhere.

As mentioned elsewhere, the other option is to:

Which is just as good, and probably more performant.

However , all that said, ideally this should only be handled in the consuming service. If the value is empty, the consumer (whether a view or another client [like javascript]) should be allowed to make this choice on it's own. As, in actuality, the semantic data is empty for the model. How this is handled should be up to the consumer it's self, ie, if this is going to a template/view, the conditional should be handled during display. If it is sent as JSON, the client should be able to make the choice.

You are asking about styles , that is probably the most important. The best style is, if you are providing data to a client, don't fake it (but document the possible empty response).

Mike's user avatar

  • \$\begingroup\$ Great answer, and nobody had seen this before. So you asked about the syntax errors. Say you write "['with a really long name'][and multiple']". If this wasn't in a PHP string, but actually interpreted by PHP as PHP code, you would get a meaningful error, but in your function the regex would simply fail, I guess? \$\endgroup\$ –  Quentin Pradet Commented Jan 7, 2015 at 21:02
  • \$\begingroup\$ It would, you are correct. I will think on how to make that not suck. \$\endgroup\$ –  Mike Commented Jan 7, 2015 at 22:12
  • \$\begingroup\$ You could send an array of strings instead. Not sure this is worth thinking about, though! \$\endgroup\$ –  Quentin Pradet Commented Jan 8, 2015 at 7:52
  • \$\begingroup\$ @mickmackusa - very good point! I kind of blindly include those flags in most all of my regular expressions just because of the way I am usually using them. That said, you are correct that they have NO impact on the expression at hand. Fixed. \$\endgroup\$ –  Mike Commented Oct 27, 2022 at 17:32

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php assign if undefined

PHP Tutorial

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Variables are "containers" for storing information.

Creating (Declaring) PHP Variables

In PHP, a variable starts with the $ sign, followed by the name of the variable:

In the example above, the variable $x will hold the value 5 , and the variable $y will hold the value "John" .

Note: When you assign a text value to a variable, put quotes around the value.

Note: Unlike other programming languages, PHP has no command for declaring a variable. It is created the moment you first assign a value to it.

Think of variables as containers for storing data.

A variable can have a short name (like $x and $y ) or a more descriptive name ( $age , $carname , $total_volume ).

Rules for PHP variables:

  • A variable starts with the $ sign, followed by the name of the variable
  • A variable name must start with a letter or the underscore character
  • A variable name cannot start with a number
  • A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
  • Variable names are case-sensitive ( $age and $AGE are two different variables)

Remember that PHP variable names are case-sensitive!

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Output Variables

The PHP echo statement is often used to output data to the screen.

The following example will show how to output text and a variable:

The following example will produce the same output as the example above:

The following example will output the sum of two variables:

Note: You will learn more about the echo statement and how to output data to the screen in the PHP Echo/Print chapter .

PHP is a Loosely Typed Language

In the example above, notice that we did not have to tell PHP which data type the variable is.

PHP automatically associates a data type to the variable, depending on its value. Since the data types are not set in a strict sense, you can do things like adding a string to an integer without causing an error.

In PHP 7, type declarations were added. This gives an option to specify the data type expected when declaring a function, and by enabling the strict requirement, it will throw a "Fatal Error" on a type mismatch.

You will learn more about strict and non-strict requirements, and data type declarations in the PHP Functions chapter.

Variable Types

PHP has no command for declaring a variable, and the data type depends on the value of the variable.

PHP supports the following data types:

  • Float (floating point numbers - also called double)

Get the Type

To get the data type of a variable, use the var_dump() function.

The var_dump() function returns the data type and the value:

See what var_dump() returns for other data types:

Assign String to a Variable

Assigning a string to a variable is done with the variable name followed by an equal sign and the string:

String variables can be declared either by using double or single quotes, but you should be aware of the differences. Learn more about the differences in the PHP Strings chapter .

Assign Multiple Values

You can assign the same value to multiple variables in one line:

All three variables get the value "Fruit":

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How to Fix PHP Notice: Undefined Variable

Introduction.

Encountering a notice that says ‘Undefined Variable’ in PHP is a common issue that arises when developing or maintaining PHP code. This notice is generated by PHP when you attempt to use a variable that has not been set or defined; in other words, if the variable does not exist or was never assigned a value.

The ‘Undefined Variable’ notice is not a fatal error and does not stop the script from running. However, it indicates poor coding practices and might lead to unpredictable behavior or bugs in your application. Hence, it’s important to understand why this notice appears and learn how to fix it properly.

Understanding PHP Notices

PHP notices are the result of PHP’s error reporting mechanism. When you see a notice, it’s typically because your PHP configuration’s error reporting level includes E_NOTICE , which reports run-time notices. Notices are less severe than warnings ( E_WARNING ) and fatal errors ( E_ERROR ), but they give developers valuable hints about potential issues with their code.

To temporarily suppress these notices, some developers use the error_reporting function:

While this hides the notices, it does not address the underlying problem and should not be considered a solution.

The Undefined Variable Notice

An ‘Undefined Variable’ notice appears when you attempt to access or manipulate a variable that has not yet been defined. Here’s an example:

If $count has not previously been set, PHP will generate a notice.

Common Causes

1. Typographical errors in variable names. 2. Using variables before they are defined or without checking if they exist. 3. Variables set inside conditions that are not met so the code block never runs. 4. Form data that was not correctly submitted or processed. 5. Missed or incorrect function arguments.

Best Practices for Resolution

Instead of silencing the notice, you should properly fix the root cause. Here are some best practices for resolving undefined variable notices:

1. Initialize Variables

Before using a variable, always ensure that it is initialized:

2. Use isset() or empty()

Check if a variable exists using isset() or if it has a non-empty, non-zero value using empty() :

3. Use Ternary or Null Coalescing Operator

For concise code, you can use the ternary or null coalescing operator:

4. Properly Handle Form and Request variables

Make sure you always check for the existence of request variables before trying to use them:

5. Use Default Function Arguments

If a function is expecting an argument that may not be provided, set a default value for the parameter:

Development and Production Environments

In a development environment, it’s good practice to have error reporting set to the highest level by using error_reporting(E_ALL) . This configuration will ensure all potential issues are visible and can be addressed during the development process.

In a production environment, you would typically suppress error messages to the user by using error_reporting(0) and instead, log errors internally for your administrative review. This shields users from seeing unsightly error messages and provides you with a way to monitor and fix recurring issues.

Addressing PHP notices including ‘Undefined Variable’ can feel like a chore at first, but it steers you towards writing more robust, maintainable code. By following the best practices highlighted in this guide, you can ensure that the variables in your PHP scripts are always defined which helps in preventing many common bugs and issues. Moreover, keeping a clean error log allows you to spot genuine problems more readily and builds a better foundation for your PHP applications.

Ultimately, keen attention to error messages and a proactive approach to fixing them will enhance the reliability and quality of your web applications, leading to a better end-user experience.

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[Solved]: Notice: Undefined variable in PHP

The fix for undefined variable error, 1. define your variables before using them, 2. validating variables with isset() function, 3. setting the undefined variable to a default value, 4. disabling notice error reporting, you may also like:, quick links.

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  • What are common causes of undefined variable errors in PHP and how can I fix them?

Hey everyone, I hope you're doing well. I'm relatively new to PHP programming and I've encountered an issue with undefined variable errors that I just can't seem to resolve. I've searched around for solutions but I'm still struggling, so I thought I'd reach out to this forum for some guidance. To give you some context, I'm currently working on a PHP project where I'm trying to access the value of a variable that I've declared but keep getting an "undefined variable" error. I'm not sure what I'm doing wrong or what the common causes of this error are. Could someone please help me understand why this error occurs and how I can fix it? I'd greatly appreciate any insight or suggestions you can provide. Thanks in advance!

All Replies

dhaley

Hey there, I totally understand the frustration that comes with encountering undefined variable errors in PHP. It can be a tricky issue to tackle, but I'll try to share my experience and offer some advice. One common cause of this error is variable scoping. PHP variables have different scopes, such as global, local, and function scopes. If you're trying to access a variable that was declared within a function or another block, you might encounter an undefined variable error when trying to access it outside of that scope. To fix this, you can either declare the variable globally or pass it as a parameter to the desired function. Another situation where I've encountered this error is when I forgot to initialize the variable before using it. PHP requires variables to be initialized before they can be used. If you attempt to use an uninitialized variable, it will result in an undefined variable error. A quick fix for this is to assign a default value to the variable when declaring it. A rookie mistake that can lead to this error is misspelling a variable name. For example, if you mistakenly type "$usreName" instead of "$userName", PHP will treat it as a new variable and throw an undefined variable error. Double-checking your variable names and ensuring they match throughout your code can save you from unnecessary errors. Lastly, enabling error reporting in PHP can be incredibly helpful in identifying and debugging such errors. By setting the error reporting level to "E_ALL," PHP will display all types of errors, including undefined variable errors, making it easier to pinpoint the problem areas in your code. I hope sharing my experiences helps you troubleshoot your undefined variable issue. If you have any further questions, please feel free to ask. Good luck!

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ashanahan

Hey there, I've faced this issue before, and it can be quite frustrating. The "undefined variable" error happens when you try to use a variable that hasn't been declared or defined yet within the scope where you're using it. There could be a few common causes for this error. One possibility is that you misspelled the variable name when you declared it, or you forgot to declare it altogether. So, double-check your code and make sure you've declared the variable with the correct spelling. Another common cause is that you're trying to access the variable outside of the scope where it was defined. PHP variables have a limited scope, so they are only accessible within the block or function where they were declared. If you're trying to use the variable outside of that scope, you'll encounter an undefined variable error. Make sure you're accessing the variable within the correct scope or consider using global variables if necessary. Additionally, it's possible that the variable is defined within a conditional statement or loop, and you're trying to access it outside of that block. In such cases, the variable is only available within the specific block where it was defined. To resolve this, you can declare the variable before the conditional statement or loop, giving it a default value, so it is accessible outside of the block. To fix the undefined variable error, you can initialize the variable with a default value before using it or ensure that you've properly declared it within the appropriate scope. You can also enable error reporting in PHP by adding the following line at the beginning of your script or in your php.ini file: php error_reporting(E_ALL); This will help you identify other potential errors that may be affecting your code. I hope this helps you fix the issue! If you have any further questions, feel free to ask.

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How To Remove Undefined Variable Error In PHP

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Introduction

Welcome to this guide on how to remove the “undefined variable” error in PHP. As a PHP developer, you may have encountered this common error when running your code. It can be frustrating and time-consuming to debug, but fear not – we are here to help you understand the error and provide practical solutions to resolve it.

PHP is a versatile and widely used server-side scripting language that offers powerful features for web development. However, one of the challenges developers often face is dealing with undefined variable errors. These errors occur when you try to use a variable that has not been defined or initialized. They can cause your code to break and prevent your application from functioning as intended.

In this guide, we will explore the concept of variable scope in PHP, which is crucial to understanding why undefined variable errors occur. We will also cover various methods for debugging and resolving these errors, ranging from using built-in functions and operators to implementing best practices in your coding practices to prevent such errors from occurring in the first place.

Removing undefined variable errors in your PHP code will not only improve the overall functionality of your website or application but also ensure a smoother user experience. It will help you deliver reliable and error-free solutions to your clients or users.

Throughout this guide, we will provide clear examples and practical solutions to help you become proficient at handling undefined variable errors. So, let’s dive in and conquer this common issue together!

What is an Undefined Variable Error?

An undefined variable error in PHP occurs when you try to use a variable that has not been declared or initialized. It happens when you reference or perform operations on a variable that does not exist in the current scope. This error can be a common and frustrating issue for PHP developers, especially those new to the language.

In PHP, variables are used to store values that can be accessed and manipulated throughout the code. However, before using a variable, it must be declared and assigned a value. If you attempt to use a variable that has not been defined, PHP will raise an undefined variable error.

The most common scenario for encountering this error is when you forget to initialize a variable or misspell its name. For example, if you attempt to echo the value of a variable without defining it first, PHP will throw an undefined variable error.

It’s important to note that PHP has different levels of variable scope, which determines where a variable can be accessed within a program. Variables can be defined as global variables, accessible from any part of the script, or local variables, restricted to a specific function or block of code. Understanding variable scope is crucial for resolving undefined variable errors since accessing a variable outside of its scope will trigger this error.

Undefined variable errors can disrupt the execution of your code and result in unexpected behavior. They can be tricky to debug, especially in larger codebases or complex applications. However, with a clear understanding of variable scope and knowledge of effective debugging techniques, you can quickly identify and resolve these errors, ensuring the smooth execution of your PHP code.

Understanding Variable Scope in PHP

Variable scope in PHP refers to the accessibility and visibility of variables within different parts of your code. Understanding variable scope is crucial for writing organized and error-free PHP programs.

PHP has three main levels of variable scope: global scope, local scope, and function scope.

Global scope refers to variables that are declared outside of any functions or methods. These variables can be accessed and manipulated from anywhere within your PHP script. However, it’s important to use global variables sparingly as they can make your code more difficult to maintain and debug.

Local scope refers to variables that are declared inside a function or a block of code, such as a loop or conditional statement. These variables are only accessible within the specific function or block where they are defined. Once the function or block execution completes, the variables are destroyed and cannot be accessed in other parts of the code.

Function scope is similar to local scope but specifically applies to variables declared within a function. Function parameters and variables defined inside the function are only accessible within that function, and they are discarded once the function execution terminates.

It’s worth noting that variables declared within nested functions have access to variables defined in their parent functions. This is known as variable inheritance or variable chaining. However, variables declared in a nested function are not accessible in its parent or sibling functions.

Understanding variable scope in PHP is essential for preventing undefined variable errors. When you encounter an undefined variable error, it’s often because you are trying to access a variable from an incorrect scope, such as using a local variable outside of its function or referencing a global variable within a function without properly declaring it as global.

In the next sections, we’ll discuss various debugging techniques and best practices to help you handle undefined variable errors effectively in your PHP code. By following these practices and understanding the scope of your variables, you can minimize the likelihood of encountering these errors and improve the quality and reliability of your PHP applications.

Debugging an Undefined Variable Error

Debugging an undefined variable error in PHP involves identifying the source of the error and taking the necessary steps to resolve it. Here are some effective techniques and tools you can use to debug these errors and ensure smooth code execution.

1. Enable error reporting: By default, PHP doesn’t display undefined variable errors. To enable error reporting, add the following lines of code at the beginning of your PHP script:

php ini_set(‘display_errors’, 1); ini_set(‘display_startup_errors’, 1); error_reporting(E_ALL);

With error reporting enabled, PHP will display any undefined variable errors on the screen, making it easier for you to identify and fix them.

2. Inspect the error message: When an undefined variable error occurs, PHP will provide an error message with the line number and file where the error occurred. Use this information to locate the specific line of code causing the error.

3. Check for misspelled variable names: Double-check the variable names in your code and ensure they are spelled correctly. Even a small typo can lead to an undefined variable error. Pay close attention to capitalization as PHP is case-sensitive.

4. Verify variable scope: Make sure that the variable you’re trying to access is within the correct scope. If you’re trying to access a local variable outside of a function, it will result in an undefined variable error. Similarly, if you’re referencing a global variable inside a function, you need to use the global keyword to make it accessible.

5. Use var_dump() or print_r() for debugging: If you’re unsure whether a variable is defined or what its value is, use the var_dump() or print_r() functions to display the variable’s contents. These functions are invaluable for checking the existence and value of variables during the debugging process.

6. Use conditional statements: Use conditional statements to check if a variable is defined before using it. The isset() function is especially useful for checking the existence of a variable. Here’s an example:

php if (isset($variable)) { // Use the variable here } else { // Handle the situation when the variable is not defined }

By performing these checks, you can prevent undefined variable errors from occurring and gracefully handle situations where the variable is not defined.

Debugging undefined variable errors requires a systematic approach and attention to detail. By following these techniques and taking a closer look at your code, you’ll be able to identify and fix these errors more effectively, providing a stable and error-free experience for your users.

Using isset() Function to Check Variable Existence

In PHP, one of the most widely used functions for checking variable existence is isset() . It allows you to determine whether a variable has been defined and is not null. By using isset() to check the existence of a variable, you can effectively prevent undefined variable errors in your code.

The isset() function takes one or more parameters and returns true if all the specified variables are set and not null. If any of the variables are undefined or null, the function returns false . This allows you to conditionally execute code based on the existence of a variable.

Here’s an example that demonstrates how to use isset() to check if a variable is defined before using it:

php if (isset($variable)) { // The variable is defined, so you can safely use it here } else { // The variable is not defined, handle the situation accordingly }

By using isset() , you prevent PHP from throwing an undefined variable error and provide a safeguard against unexpected behaviors in your code. You can include additional logic within the condition to handle situations where the variable is not defined.

It’s important to note that isset() returns false even if the variable exists but its value is null . To check if a variable is both defined and not null , you can use the !== operator. Here’s an example:

php if (isset($variable) && $variable !== null) { // The variable is defined and not null, so you can safely use it here } else { // The variable is either undefined or null, handle the situation accordingly }

By combining the isset() function with the !== operator, you can ensure that a variable is both defined and holds a non-null value before using it in your code.

Using the isset() function is a best practice when working with variables in PHP. It helps you handle situations where variables might be undefined, preventing errors and providing more robust code. By incorporating isset() checks in your code, you can improve the reliability and maintainability of your PHP applications.

Using the @ Operator to Suppress Errors

In PHP, the @ operator can be used to suppress error messages, including undefined variable errors. It allows you to perform operations on variables without generating error messages, effectively ignoring any undefined variable errors that may occur.

The @ operator is placed in front of a line of code or an expression that may generate an error. When used, PHP will not display any error messages that occur within the scope of that specific line of code. This can be useful in scenarios where you expect potential errors and want to handle them in a specific way or ignore them altogether.

Here’s an example that demonstrates how to use the @ operator to prevent undefined variable errors:

php $value = @$undefinedVariable; // The undefined variable error is suppressed // You can handle the situation accordingly without the error interrupting the flow

By prefixing the variable assignment with @ , PHP will not raise an error if the variable is undefined. Instead, the $value variable will be assigned a value of null , allowing you to handle the situation without the error interrupting the flow of your program.

While using the @ operator can be a quick way to suppress errors, it is generally considered a bad practice. It can make your code harder to debug and maintain because it hides potential issues. When errors are suppressed, it becomes more difficult to identify and fix issues in your code, leading to potential bugs and inconsistencies.

Instead of relying on the @ operator, it is recommended to use proper error handling techniques, such as checking variable existence with isset() before using them, or implementing try-catch blocks to catch and handle specific exceptions. These techniques provide more granular control over error handling and allow you to handle different scenarios in a more structured manner.

In summary, while the @ operator can be used to suppress errors like undefined variable errors, it is generally discouraged due to its impact on code maintainability and bug detection. It’s best to use proper error handling techniques and ensure variables are properly defined and initialized to avoid such errors in the first place.

Declaring Variables with Default Values

To prevent undefined variable errors in PHP, it’s recommended to declare variables with default values. This ensures that the variables have a valid initial value, even if one is not explicitly assigned. By providing default values, you can avoid undefined variable errors and ensure a more predictable behavior of your code.

When declaring a variable, you can assign it a default value using the assignment operator ( = ). This value will be used if no other value is explicitly assigned to the variable. Here’s an example:

php $variable = “default value”;

In the above example, the $variable is initialized with the default value of “default value”. If no other value is assigned to it, it will retain this default value throughout your code.

Declaring variables with default values has several advantages. Firstly, it eliminates the possibility of encountering undefined variable errors since the variable will always have a defined value. This leads to more reliable code execution and reduces the need for error handling related to undefined variables.

Secondly, it enhances the readability of your code. By declaring variables with default values, other developers (including yourself) who read your code can easily understand the purpose and expected value of the variable. It provides a clear indication of what the variable represents and how it is intended to be used.

However, it’s important to choose appropriate default values based on the context and requirements of your code. The default value should make logical sense in relation to the purpose of the variable. For example, if the variable represents a counter, a default value of 0 might be appropriate. Similarly, if the variable represents a user’s name, a default value of an empty string (“”) can be considered.

By consistently declaring variables with default values, you can improve the robustness and readability of your PHP code. It helps prevent undefined variable errors and ensures that variables always have an expected initial value, providing a more stable foundation for your applications.

Checking Variable Existence with the null coalescing operator

Introduced in PHP 7, the null coalescing operator ( ?? ) provides a concise way to check for variable existence and assign default values if the variable is undefined. It allows you to streamline your code by combining variable existence checks and default value assignment into a single expression.

The null coalescing operator works by returning the value of the left-hand operand if it exists and is not null. If the left-hand operand is undefined or null, it returns the value of the right-hand operand. Here’s an example:

php $variable = $undefinedVariable ?? “default value”; // If $undefinedVariable is defined and not null, $variable will hold its value // If $undefinedVariable is undefined or null, $variable will be assigned the “default value”

In the above example, the null coalescing operator checks if the $undefinedVariable exists and is not null. If it does exist and is not null, its value is assigned to $variable . Otherwise, $variable is assigned the default value of “default value”.

The null coalescing operator can be used to simplify your code by providing a concise and readable way to handle variable existence checks and default value assignment, all in one line. It reduces the need for separate isset() checks or conditional statements, resulting in cleaner and more efficient code.

It’s important to note that the null coalescing operator can only be used to assign a default value if the variable is undefined or null. It cannot be used to assign a default value based on other conditions. For more complex scenarios, you may still need to use conditional statements or other techniques.

The null coalescing operator is a powerful addition to PHP, providing a convenient way to handle variable existence and default value assignment. By leveraging this operator, you can write more concise and readable code, reducing the likelihood of encountering undefined variable errors.

Using Global Keyword to Access Global Variables within a Function

In PHP, variables that are declared outside of any function or class have global scope. Global variables can be accessed and modified from anywhere within the script. However, when working with functions, variable scoping rules come into play, and accessing global variables within a function requires the use of the global keyword.

When you declare a variable within a function with the same name as a global variable, PHP treats it as a separate local variable, creating a new scope. To access the value of the global variable within the function, you need to use the global keyword followed by the variable name. Here’s an example:

php $globalVar = “Hello, global!”;

function printGlobalVar() { global $globalVar; echo $globalVar; // Output: Hello, global! }

In the above example, the global keyword is used to access the $globalVar variable within the printGlobalVar() function. Without the global keyword, PHP would create a new local variable with the same name, shadowing the global variable and not affecting its value.

It’s important to note that the use of global variables should be limited to cases where it’s absolutely necessary. Overusing global variables can make your code less maintainable and harder to debug. It’s generally considered a best practice to pass variables as function arguments or use techniques like dependency injection to avoid excessive reliance on global state.

Additionally, modifying global variables within a function can lead to unexpected behaviors and make your code harder to reason about. It is advisable to favor encapsulation and use local variables within functions whenever possible.

By using the global keyword, you can access and work with global variables within your PHP functions. However, it is crucial to use global variables judiciously and consider alternative approaches that promote encapsulation and modularization of your code.

Best Practices to Avoid Undefined Variable Errors

Undefined variable errors can be a common source of frustration for PHP developers, but there are several best practices you can follow to prevent these errors from occurring in your code. By adopting these practices, you can improve the reliability and maintainability of your PHP applications.

1. Always initialize variables: Make it a habit to initialize variables with default values, even if they are expected to be assigned a different value later. This ensures that variables have a defined value from the start and avoids undefined variable errors.

2. Use variable scoping effectively: Understand the concept of variable scope in PHP and ensure that variables are declared within the appropriate scope. Avoid using global variables where they’re not necessary, and instead pass variables as function parameters or use object-oriented techniques for encapsulation.

3. Check variable existence before usage: Use functions like isset() or the null coalescing operator ( ?? ) to check if a variable is defined before using it. This prevents undefined variable errors and allows you to handle situations where the variable is not defined gracefully.

4. Enable error reporting: Ensure that error reporting is enabled in your PHP configuration during development. This helps you identify and fix undefined variable errors by displaying error messages that highlight their occurrences in your code.

5. Use proper debugging techniques: When encountering undefined variable errors, analyze the error messages and stack traces to pinpoint the source of the error. Utilize tools like var_dump() or print_r() to inspect variables and identify where they are not properly defined.

6. Adhere to coding standards and naming conventions: Consistent naming conventions help you avoid typographical errors and improve code readability. Naming variables meaningfully and following a standard naming convention reduces the likelihood of misspelling or misreferencing variables, which can lead to undefined variable errors.

By following these best practices, you can significantly reduce the occurrence of undefined variable errors in your PHP code. These practices promote cleaner and more reliable code, making your applications more robust and easier to maintain in the long run.

In PHP development, dealing with undefined variable errors is a common challenge, but it can be overcome with proper understanding and implementation of best practices. By grasping the concept of variable scope and utilizing techniques such as initializing variables, checking for variable existence, and using the global keyword when necessary, you can prevent and handle undefined variable errors effectively.

Enabling error reporting and using debugging techniques are essential for identifying and resolving undefined variable errors in your code. Additionally, incorporating proper coding standards and naming conventions helps minimize errors by ensuring consistent variable usage and reducing misspellings or misreferences.

Remember, it is crucial to strike a balance between preventing undefined variable errors and not overusing global variables. Overreliance on global state can lead to code that is harder to maintain and debug. Instead, favor encapsulation and use local variables within functions whenever possible.

By implementing these best practices and following a disciplined approach to PHP development, you can minimize the occurrence of undefined variable errors and enhance the reliability and maintainability of your PHP applications. Happy coding!

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@JeffreyWay

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You know how, in JavaScript, we can set a value to a variable if one doesn't, like this:

This is quite common and very helpful. Another option is to do:

Well, in PHP, that doesn't work. What many do is:

Which works...but it's a bit verbose. My preference, at least for checking for empty strings, is:

What's your preference for setting values if they don't already exist?

@isimmons

isimmons commented Jul 28, 2012

@JeffreyWay I like the last option as long as the var has a default set like in your example function to avoid the undefined variable message. Or shorten it to one line by doing it this way.

return $name ? $name : 'joe';

If the variable isn't set to '' by default it doesn't seem like there would be a way around using isset() to avoid the warning.

Sorry, something went wrong.

@avinashz

avinashz commented Jul 29, 2012

if(!isset($name)){ $name = 'joe'}

@everzet

everzet commented Jul 29, 2012

@zecho well, in case of default argument with = null , you don't need isset(...) check - you just need $name = $name ?: 'default' . I was talking bout that.

@zecho

zecho commented Jul 30, 2012

@everzet , you're not right again. When $var === null your statement generates notice 'Undefined variable' because doesn't make difference between null and undefined.

everzet commented Jul 30, 2012

@zecho nope, here i'm absolutely right:

will output:

$var === null means that variable is defined (its value is null ).

@zecho no, you try. No exceptions/notices/errors for me :)

do this outside a function/method. I won't explain you what's the difference in php between function parameter and a variable. Also put as first line in the function

to see the result when $name = null

I don't get what you're trying to prove here, but please, explain me the difference in php between function parameter and variable.

@zecho also, i think you've started arguing about https://gist.github.com/3194444#gistcomment-381958 Please re-read it again, cuz it looks like we have misunderstanding here.

@everzet , sorry about misunderstanding, I didn't read properly this comment. The idea is that you can't use $name = $name ?: 'default' when variable is not initialized at all (even with $name = null ).

@zecho yep, and here is the source misunderstanding:

... even with $name = null

$name = null initializes variable. With null value.

var_dump($name); is a proper statement and will return:

Without any exception/notice. And

Will successfully output

Without any exception/notice. Because null is a proper value of any variable.

@avioli

avioli commented Jul 31, 2012

Just my 20 cents - null initialises the variable with nothing. It prepares the variable to be garbage collected in the next cycle. It only does the following - puts it in the current scope so the interpreter is not considering it not existing. It's similar to what global $global_var; does.

var_dump( isset( $null_var ) ); will output bool(false) anyway.

Setting a variable to null is only useful for cases as with the one you circle around @everzet - having it as a function's default variable.

@RodrigoEspinosa

RodrigoEspinosa commented Aug 1, 2012

I think the best way is: $name = (isset($name)) ? $name : "joe"; very similar to name || (name = 'joe');

@banago

banago commented Aug 5, 2012

Jeffrey, guess what, you can do the same thing on PHP:

$myValue = $someOtherValue ?: true;

http://www.selfcontained.us/2010/11/30/php-coalesce/

@Krknv

Krknv commented Jan 16, 2015

$item = isset($arr["super_long_key_name"]) ? $arr["super_long_key_name"] : "default"; $item =@ $arr["super_long_key_name"]) ?: "default";

@agaezcode

agaezcode commented Mar 6, 2015

php Echo number if the number is not zero.

@fvzsf65536

fvzsf65536 commented May 4, 2015

isset($name) || $name = 'Joe';

!empty($name) || $name = 'Joe';

fvzsf65536 commented May 7, 2015

$name = $name ?? 'Joe';

@waspinator

waspinator commented Oct 6, 2015

How would you do it in an array?

@3642066

3642066 commented Jan 1, 2016

I just used : if ( empty($name) ) $name = 'joe'; This is more a kind of "human readable", for me . I used for setting the opacity of a php image processing app, so i can update the main app later, because i'm using a slider input on app test version but i still using the same URL for processing the images, with caused bug because of a missing variable (opacity) . Thank you .

@eness

eness commented May 4, 2016

Here is the perfect solution I've found and been using for a while ..

This will print John if $name is not empty but if $name is empty, it will print out 'User has no name' instead, which acts like a default value.

@nwpray

nwpray commented Aug 15, 2016 • edited Loading

Best way is always the ternary operators. Sorry to open this up again, but I spent a good 20 min testing out cases because this conversation did so many loops through multiple techniques but didn't appear to settle.

and an example:

I settled on this because it appeared to be the most versatile. You can set a default value and if your using a false evaluating value as the default its easy to see if the variable was set. a.k.a. in this example if I do:

I know that the value is not set and if I want to check if it is set:

And it may be a bit verbose but you can do it all in one swoop like this:

And like has been said, you can shorthand the ternary and just use:

But you will get a notice thrown on array value not set so I always just use isset and assign a value in the ternary to avoid silencing messages for no reason.

@RedSparr0w

RedSparr0w commented Sep 12, 2017 • edited Loading

I know this is a very old thread but,

with php 7+ you can use something like the following:

assigned as will return
User not set
User not set
User not set
User not set
John

?? checks if the value is undefined or null ?: checks if the value is null or false or an empty string

@robrecord

robrecord commented Oct 9, 2018 • edited Loading

RedSparr0w you can shorten this:

@sobujbd

sobujbd commented Jun 4, 2019

Finally, I prefer...

Usages: get_string($name, "Unknown");

@axelitus

axelitus commented Jun 18, 2019

This all be over once PHP 7.4 arrives:

@ben221199

ben221199 commented Sep 1, 2019

Does it throw warnings?

Will generate this:

@str

str commented May 24, 2023

Since PHP 7.4 we can now easily just say:

How to solve PHP undefined index notice

php assign if undefined

The Notice: Undefined index message means that the index key you use to access an array’s value doesn’t exist.

Remove the undefined index notice

While the notice message is useful, you may want to turn it off in production environment so your visitors won’t see it.

Take your skills to the next level ⚡️

Undefined Variable since PHP 8.0

The code bellow worked for quite some time, but after changing the php version to 8.0, I get the error 'undefined variable on ‘$os’ and many other parts of my code. What can this be?

That’s because if none of your two conditions is true, $os is not defined. You need to set it to a default value at the outset.

Hi Moonwalk, thanks for your input. Your solution does work. I use this logic in many places. I am wondering why I get all these errors now, and not before. I also set the php version back to an earlier one, but it doesnt do the trick. Any ideas there?

It looks like this does not work anymore:

Is that correct? What is the equivalent that works??

What is $object , without any context, we cannot tell what’s wrong.

:frowning:

When you type

It will now give an error if $os doesn’t exist. Th same with:

It didnt throw an error in php 7.4 / Kirby 3.7 I didnt see it between the list changes of Kirby 3.8? When I update to php 8 and kirby 3.8 It throws the error. Any ideas?

It works as an equivalent of isset($object) I just learned.

Should I change this everywhere now?

PHP 8.0 is a lot stricter than PHP 7.4. You should never have any undefined variables. It says in the changelog that you need to change your template code to make it compatible with PHP 8+.

just to be clear, trying to access an undefined variable was also “wrong” in PHP 7, it generated an error message at the “NOTICE” level. In PHP 8 it now generates a “WARNING”; also the default error reporting level in PHP 8 has been set to “E_ALL”, while, before, by default it wouldn’t show "NOTICE"s.

Anyway, I guess you can choose between always setting a variable before using it (The Right Way™), or just provide a fallback value via the null coalescing operator when accessing the variable:

:dizzy:

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South Carolina State University

SC State begins residence hall room assignments for Fall 2024 semester

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Students on the housing waitlist also have been instructed to monitor their university email accounts for updates.

ORANGEBURG, S.C. – South Carolina State University on Friday, July 19, began assigning residence hall rooms to students who applied for housing before the June 10 deadline.

The placement process will continue into next week.

The administration will continue to communicate with other students who have been placed on a waitlist about housing needs and options.

All students are encouraged to monitor their SC State email accounts for updates.

Students will receive notifications through the StarRez residency management software, which SC State implemented this spring to more efficiently process housing applications, make room assignments, track room inventory and communicate with residents,.

President Alexander Conyers said such controls are especially important because of the interest from prospective students -- more than 12,500 new students have applied for admission to the university for the Fall 2024 Semester -- while residential space is limited both on and off campus.

“SC State is in high demand because of the quality education we provide and our vibrant HBCU culture,” Conyers said. “We simply do not have the residential capacity to accommodate all requests.

“StarRez has allowed us to systematically manage the university’s housing placements and vacancies in real time rather than through cumbersome manual data entry and tracking,” SC State President Alexander Conyers said. “We expect placement this fall to be efficient with open lines of communication to students and their families.”

SC State has 1,324 beds available on campus for the fall, along with another 830 beds in off-campus facilities leased by the SC State Housing Foundation for a total of 2,154 beds.

So, until more housing is available, the university is strategically managing its enrollment, but SC State also is working on several fronts to reduce the housing crunch.

Current and future housing initiatives

Queens Village

SC State hopes to complete three renovation projects in time for the Fall 2025 Semester:

  • Sojourner Truth Hall’s $15 million overhaul. The 14-story residence hall will provide 384 beds.
  • Rehabilitating the long-vacant Queens Village apartment complex will provide room for 40 students.
  • SC State is requesting assistance from the state of South Carolina to remodel Rowe and Nix Halls, which will provide up to 58 beds.

Other housing developments:

  • The university also is in the initial planning phase for a 500-bed residential complex on campus.
  • Orangeburg’s Railroad Corner project includes a student residential complex in which the SC State Housing Foundation will lease space.
  • Private developers will soon break ground for two new student housing complexes on Russell Street. Coupled with the residential space at Railroad Corner, the Russell Street complexes will free up residence hall rooms on the SC State campus, allowing the university to admit and house more students.

Online freshman cohort

For the Fall 2024 Semester, SC State has limited the number of freshmen who can be housed in residence halls. The university has developed, however, an online cohort that will allow additional first-year students to complete their first semester of coursework virtually.

The cohort is designed for eligible students interested in saving money while still engaging with professors, peers and campus activities and staying on track for success.

“The COVID-19 pandemic forced educators to find alternative ways of reaching students,” Conyers said. “Those experiences have offered us insight into what does and does not work in a virtual learning environment, and we have applied those lessons to this cohort.

“Most if not all these incoming students had exposure to online learning during the pandemic, so they, too, know what it takes to succeed in the virtual classroom,” Conyers said.

The online cohort will allow the university to admit more first-year students while maintaining more residential space for returning students. Students eligible for the cohort are being contacted by SC State's Division of Enrollment Management.

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Using undefined property in php class

when i run this code, output the result 8 .

but when i add __set() function, it output a notice, and not 8 output

PHP Notice: Undefined property: a::$test in /usercode/file.php on line 13

why is it happening?

Kevin Kopf's user avatar

  • 2 Maybe check the manual? –  jeroen Commented Jan 25, 2018 at 9:23
  • First define $test variable in constructor and then assign $this->test="8"; hope it will work –  Soniya Basireddy Commented Jan 25, 2018 at 9:29
  • 1 Because that's what __set does . By default, PHP will create properties on the fly. If you've defined __set and it doesn't then set the property within the method, then the property won't exist, and will raise a notice when you try and read it. –  iainn Commented Jan 25, 2018 at 9:30
  • 1 I have no idea where line 13 is –  Scuzzy Commented Jan 25, 2018 at 9:30
  • @Scuzzy sorry,in “return $this->test;” –  Deqin Chen Commented Jan 25, 2018 at 9:38

3 Answers 3

As per the docs

__set() is run when writing data to inaccessible properties.

Since you do not have anything in your __set body, the property is not created and therefore not available. You have to define the method body.

Now THAT outputs 8 .

Update You are asking why the first block of code works and the second does not. Take a look at PHP source code here and you will see the explanation in the code itself.

Looks to me, that when you do not have __set() in your class and you do $this->test , PHP internally calls it's own __set() , which does exactly what it does: sets the property name to certain value .

But when you define __set() with empty body, it overrides the default internal __set() and does nothing. And that is the main reason for your code to fail - the requested property has not been set neither by your __set() , nor by the internal one.

  • Thank you for your answer. I understand what you said. But I want to know why my first program can run successfully. Is there any official explanation? –  Deqin Chen Commented Jan 25, 2018 at 9:52
  • @DeqinChen I actually updated my answer, linking to PHP source code as well, so that you could see the reason for yourself. –  Kevin Kopf Commented Jan 25, 2018 at 11:20

When a::out() runs, there is no $test property in the object. This is why $this->test = 8; invokes a::__set() .

But a::__set() doesn't create the $test property and the next statement ( return $this->test; ) cannot find it and produces the notice.

You should declare the object properties in the class definition and initialize them in the constructor (if appropriate):

Without __set() being defined, the statement $this->test = 8; creates the $test property of the current object if it is not already created (by its definition or by a previous assignment to it) then stores 8 into it.

When __set() is defined, any attempt to set a property that doesn't exist or it is not accessible (setting inside the class a private property inherited from the parent class or setting a protected or private property outside the class) is handled by __set() . Your implementation of __set() doesn't create the missing property and it basically turns the statement $this->test = 8; into a no-op.

axiac's user avatar

  • Thank you for your answer. I understand what you said. But I want to know why my first program can run successfully. Is there any official explanation? –  Deqin Chen Commented Jan 25, 2018 at 9:50
  • @DeqinChen I updated the answer. Also read the documentation of __set() . –  axiac Commented Jan 25, 2018 at 10:02
  • 1 __set IS invoked but it does not do anything, therefore, nothing is set. Thus the warning on the return . –  Raph Commented Jan 25, 2018 at 10:45

The following is true.

you should look at is php overloading

Find the answers in the manual.

winlans's user avatar

  • Thank you for your answer. I understand what you said. But I want to know why my first program can run successfully. Is there any official explanation? –  Deqin Chen Commented Jan 25, 2018 at 9:51

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php assign if undefined

  • Language Reference

An array in PHP is actually an ordered map. A map is a type that associates values to keys . This type is optimized for several different uses; it can be treated as an array, list (vector), hash table (an implementation of a map), dictionary, collection, stack, queue, and probably more. As array values can be other array s, trees and multidimensional array s are also possible.

Explanation of those data structures is beyond the scope of this manual, but at least one example is provided for each of them. For more information, look towards the considerable literature that exists about this broad topic.

Specifying with array()

An array can be created using the array() language construct. It takes any number of comma-separated key => value pairs as arguments.

The comma after the last array element is optional and can be omitted. This is usually done for single-line arrays, i.e. array(1, 2) is preferred over array(1, 2, ) . For multi-line arrays on the other hand the trailing comma is commonly used, as it allows easier addition of new elements at the end.

Note : A short array syntax exists which replaces array() with [] .

Example #1 A simple array

The key can either be an int or a string . The value can be of any type.

  • String s containing valid decimal int s, unless the number is preceded by a + sign, will be cast to the int type. E.g. the key "8" will actually be stored under 8 . On the other hand "08" will not be cast, as it isn't a valid decimal integer.
  • Float s are also cast to int s, which means that the fractional part will be truncated. E.g. the key 8.7 will actually be stored under 8 .
  • Bool s are cast to int s, too, i.e. the key true will actually be stored under 1 and the key false under 0 .
  • Null will be cast to the empty string, i.e. the key null will actually be stored under "" .
  • Array s and object s can not be used as keys. Doing so will result in a warning: Illegal offset type .

If multiple elements in the array declaration use the same key, only the last one will be used as all others are overwritten.

Example #2 Type Casting and Overwriting example

The above example will output:

As all the keys in the above example are cast to 1 , the value will be overwritten on every new element and the last assigned value "d" is the only one left over.

PHP arrays can contain int and string keys at the same time as PHP does not distinguish between indexed and associative arrays.

Example #3 Mixed int and string keys

The key is optional. If it is not specified, PHP will use the increment of the largest previously used int key.

Example #4 Indexed arrays without key

It is possible to specify the key only for some elements and leave it out for others:

Example #5 Keys not on all elements

As you can see the last value "d" was assigned the key 7 . This is because the largest integer key before that was 6 .

Example #6 Complex Type Casting and Overwriting example

This example includes all variations of type casting of keys and overwriting of elements.

Accessing array elements with square bracket syntax

Array elements can be accessed using the array[key] syntax.

Example #7 Accessing array elements

Note : Prior to PHP 8.0.0, square brackets and curly braces could be used interchangeably for accessing array elements (e.g. $array[42] and $array{42} would both do the same thing in the example above). The curly brace syntax was deprecated as of PHP 7.4.0 and no longer supported as of PHP 8.0.0.

Example #8 Array dereferencing

Note : Attempting to access an array key which has not been defined is the same as accessing any other undefined variable: an E_WARNING -level error message ( E_NOTICE -level prior to PHP 8.0.0) will be issued, and the result will be null .
Note : Array dereferencing a scalar value which is not a string yields null . Prior to PHP 7.4.0, that did not issue an error message. As of PHP 7.4.0, this issues E_NOTICE ; as of PHP 8.0.0, this issues E_WARNING .

Creating/modifying with square bracket syntax

An existing array can be modified by explicitly setting values in it.

This is done by assigning values to the array , specifying the key in brackets. The key can also be omitted, resulting in an empty pair of brackets ( [] ).

If $arr doesn't exist yet or is set to null or false , it will be created, so this is also an alternative way to create an array . This practice is however discouraged because if $arr already contains some value (e.g. string from request variable) then this value will stay in the place and [] may actually stand for string access operator . It is always better to initialize a variable by a direct assignment.

Note : As of PHP 7.1.0, applying the empty index operator on a string throws a fatal error. Formerly, the string was silently converted to an array.
Note : As of PHP 8.1.0, creating a new array from false value is deprecated. Creating a new array from null and undefined values is still allowed.

To change a certain value, assign a new value to that element using its key. To remove a key/value pair, call the unset() function on it.

Note : As mentioned above, if no key is specified, the maximum of the existing int indices is taken, and the new key will be that maximum value plus 1 (but at least 0). If no int indices exist yet, the key will be 0 (zero). Note that the maximum integer key used for this need not currently exist in the array . It need only have existed in the array at some time since the last time the array was re-indexed. The following example illustrates: <?php // Create a simple array. $array = array( 1 , 2 , 3 , 4 , 5 ); print_r ( $array ); // Now delete every item, but leave the array itself intact: foreach ( $array as $i => $value ) { unset( $array [ $i ]); } print_r ( $array ); // Append an item (note that the new key is 5, instead of 0). $array [] = 6 ; print_r ( $array ); // Re-index: $array = array_values ( $array ); $array [] = 7 ; print_r ( $array ); ?> The above example will output: Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 ) Array ( ) Array ( [5] => 6 ) Array ( [0] => 6 [1] => 7 )

Array destructuring

Arrays can be destructured using the [] (as of PHP 7.1.0) or list() language constructs. These constructs can be used to destructure an array into distinct variables.

Array destructuring can be used in foreach to destructure a multi-dimensional array while iterating over it.

Array elements will be ignored if the variable is not provided. Array destructuring always starts at index 0 .

As of PHP 7.1.0, associative arrays can be destructured too. This also allows for easier selection of the right element in numerically indexed arrays as the index can be explicitly specified.

Array destructuring can be used for easy swapping of two variables.

Note : The spread operator ( ... ) is not supported in assignments.

Useful functions

There are quite a few useful functions for working with arrays. See the array functions section.

Note : The unset() function allows removing keys from an array . Be aware that the array will not be reindexed. If a true "remove and shift" behavior is desired, the array can be reindexed using the array_values() function. <?php $a = array( 1 => 'one' , 2 => 'two' , 3 => 'three' ); unset( $a [ 2 ]); /* will produce an array that would have been defined as $a = array(1 => 'one', 3 => 'three'); and NOT $a = array(1 => 'one', 2 =>'three'); */ $b = array_values ( $a ); // Now $b is array(0 => 'one', 1 =>'three') ?>

The foreach control structure exists specifically for array s. It provides an easy way to traverse an array .

Array do's and don'ts

Why is $foo[bar] wrong.

Always use quotes around a string literal array index. For example, $foo['bar'] is correct, while $foo[bar] is not. But why? It is common to encounter this kind of syntax in old scripts:

This is wrong, but it works. The reason is that this code has an undefined constant ( bar ) rather than a string ( 'bar' - notice the quotes). It works because PHP automatically converts a bare string (an unquoted string which does not correspond to any known symbol) into a string which contains the bare string . For instance, if there is no defined constant named bar , then PHP will substitute in the string 'bar' and use that.

The fallback to treat an undefined constant as bare string issues an error of level E_NOTICE . This has been deprecated as of PHP 7.2.0, and issues an error of level E_WARNING . As of PHP 8.0.0, it has been removed and throws an Error exception.

Note : This does not mean to always quote the key. Do not quote keys which are constants or variables , as this will prevent PHP from interpreting them. <?php error_reporting ( E_ALL ); ini_set ( 'display_errors' , true ); ini_set ( 'html_errors' , false ); // Simple array: $array = array( 1 , 2 ); $count = count ( $array ); for ( $i = 0 ; $i < $count ; $i ++) { echo "\nChecking $i : \n" ; echo "Bad: " . $array [ '$i' ] . "\n" ; echo "Good: " . $array [ $i ] . "\n" ; echo "Bad: { $array [ '$i' ]} \n" ; echo "Good: { $array [ $i ]} \n" ; } ?> The above example will output: Checking 0: Notice: Undefined index: $i in /path/to/script.html on line 9 Bad: Good: 1 Notice: Undefined index: $i in /path/to/script.html on line 11 Bad: Good: 1 Checking 1: Notice: Undefined index: $i in /path/to/script.html on line 9 Bad: Good: 2 Notice: Undefined index: $i in /path/to/script.html on line 11 Bad: Good: 2

More examples to demonstrate this behaviour:

When error_reporting is set to show E_NOTICE level errors (by setting it to E_ALL , for example), such uses will become immediately visible. By default, error_reporting is set not to show notices.

As stated in the syntax section, what's inside the square brackets (' [ ' and ' ] ') must be an expression. This means that code like this works:

This is an example of using a function return value as the array index. PHP also knows about constants:

Note that E_ERROR is also a valid identifier, just like bar in the first example. But the last example is in fact the same as writing:

because E_ERROR equals 1 , etc.

So why is it bad then?

At some point in the future, the PHP team might want to add another constant or keyword, or a constant in other code may interfere. For example, it is already wrong to use the words empty and default this way, since they are reserved keywords .

Note : To reiterate, inside a double-quoted string , it's valid to not surround array indexes with quotes so "$foo[bar]" is valid. See the above examples for details on why as well as the section on variable parsing in strings .

Converting to array

For any of the types int , float , string , bool and resource , converting a value to an array results in an array with a single element with index zero and the value of the scalar which was converted. In other words, (array)$scalarValue is exactly the same as array($scalarValue) .

If an object is converted to an array , the result is an array whose elements are the object 's properties. The keys are the member variable names, with a few notable exceptions: integer properties are unaccessible; private variables have the class name prepended to the variable name; protected variables have a '*' prepended to the variable name. These prepended values have NUL bytes on either side. Uninitialized typed properties are silently discarded.

These NUL can result in some unexpected behaviour:

The above will appear to have two keys named 'AA', although one of them is actually named '\0A\0A'.

Converting null to an array results in an empty array .

It is possible to compare arrays with the array_diff() function and with array operators .

Array unpacking

An array prefixed by ... will be expanded in place during array definition. Only arrays and objects which implement Traversable can be expanded. Array unpacking with ... is available as of PHP 7.4.0.

Example #9 Simple array unpacking

Example #10 Array unpacking with duplicate key

Note : Keys that are neither integers nor strings throw a TypeError . Such keys can only be generated by a Traversable object.
Note : Prior to PHP 8.1, unpacking an array which has a string key is not supported: <?php $arr1 = [ 1 , 2 , 3 ]; $arr2 = [ 'a' => 4 ]; $arr3 = [... $arr1 , ... $arr2 ]; // Fatal error: Uncaught Error: Cannot unpack array with string keys in example.php:5 $arr4 = [ 1 , 2 , 3 ]; $arr5 = [ 4 , 5 ]; $arr6 = [... $arr4 , ... $arr5 ]; // works. [1, 2, 3, 4, 5] ?>

The array type in PHP is very versatile. Here are some examples:

Example #11 Using array()

Example #12 Collection

Changing the values of the array directly is possible by passing them by reference.

Example #13 Changing element in the loop

This example creates a one-based array.

Example #14 One-based index

Example #15 Filling an array

Array s are ordered. The order can be changed using various sorting functions. See the array functions section for more information. The count() function can be used to count the number of items in an array .

Example #16 Sorting an array

Because the value of an array can be anything, it can also be another array . This enables the creation of recursive and multi-dimensional array s.

Example #17 Recursive and multi-dimensional arrays

Array assignment always involves value copying. Use the reference operator to copy an array by reference.

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  1. php

    Before php 7 this would have given an Undefined index: foo notice. But with the null coalescing operator, that notice won't come up. But with the null coalescing operator, that notice won't come up. Share

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    It feels elegant and naughty at the same time! :) I normally only use it when assigning to another variable or return from a function, though. \$\endgroup\$ - David Harkness. Commented Jul 15, 2012 at 2:06. 7 \$\begingroup\$ Note that if your variable is undefined, PHP will throw notices about it. This, unfortunately, is no replacement for ...

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    PHP is a popular general-purpose scripting language that powers everything from your blog to the most popular websites in the world. ... Assigning a closure to a variable uses the same syntax as any other assignment, including the trailing semicolon: ... Undefined variable: message in /example.php on line 6 NULL string(5) "hello" string(5 ...

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    @Hortitude: That's point (4). I generally wouldn't typeof foo=='undefined'; it tends to be used for (4a) global-sniffing, in which case I'd prefer to be explicit and say 'foo' in window, or (4b) testing against the undefined-value itself, in which case I'd prefer to be readable and say foo===undefined.In theory testing typeof against 'undefined' could have a use case that other constructs ...

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    2. Validating variables with isset() function. Another way to go about this is to validate whether the variables have been set before using them.

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  13. PHP: Assign null if not set?

    Is there any sort of assign-if-not-empty-otherwise-assign-null function in PHP? I'm looking for a cleaner alternative to the following: ... EDIT: It should be noted that I'm trying to avoid a notice for undefined values. php; Share. Follow edited Jul 25, 2022 at 15:56. Your Common Sense ...

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    PHP: Set value if not exist. GitHub Gist: instantly share code, notes, and snippets. ... @JeffreyWay I like the last option as long as the var has a default set like in your example function to avoid the undefined variable message. Or shorten it to one line by doing it this way. ... But you will get a notice thrown on array value not set so I ...

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  17. How do I fix "Undefined variable" error in PHP?

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