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How to Pass PHP Variables by Reference and Modify Their Original Values

M66 2025-06-15

How to Pass PHP Variables by Reference and Modify Their Original Values

In PHP, you can pass variables by reference using the ampersand (&) symbol, instead of passing them by value. This allows you to modify the original variable directly within a function or method. PHP provides two ways to pass variables by reference:

  • By using the ampersand symbol in the function/method declaration
  • By passing the variable to the function and using the ampersand symbol during the function call

Using the Ampersand Symbol in Function/Method Declarations to Pass by Reference

In PHP, you can pass a variable by reference by adding the ampersand (&) symbol before the parameter in the function or method declaration. This means that you want the variable to be modified inside the function, affecting the original value. Here’s a simple example:

  
function modifyValue(&$variable) {  
    $variable += 10;  
}  

$myVariable = 5;  
modifyValue($myVariable);  
echo $myVariable;  // Output: 15

In the code above, the function modifyValue accepts a parameter $variable that has the ampersand (&) symbol before it. When $myVariable is passed to the function, it is passed by reference, so any modifications made inside the function directly affect $myVariable. Therefore, the output of echo $myVariable is the updated value 15.

Using the ampersand symbol in the function declaration is a clear and explicit way to pass variables by reference, ensuring that the original variable can be modified within the function.

Passing a Variable by Reference During Function Call

Aside from adding the ampersand symbol in the function declaration, you can also explicitly pass a variable by reference during the function call. However, it’s important to note that merely adding the ampersand symbol during the function call does not actually pass the variable by reference. In some cases, this may result in a syntax error or unexpected behavior.

  
function modifyValue($variable) {  
    $variable += 10;  
}  

$myVariable = 5;  
modifyValue(&$myVariable);  
echo $myVariable;  // Output: 5

In this example, the function modifyValue is defined without the ampersand symbol. Therefore, even though the ampersand symbol is added during the function call, $myVariable is still passed by value. The function will not modify the original variable, and the output of echo $myVariable is 5.

Conclusion

In PHP, you can pass variables by reference by either using the ampersand symbol in the function declaration or by passing the variable by reference during the function call. However, adding the ampersand symbol only during the function call will not result in passing the variable by reference. Understanding and properly using reference passing can help you better control the scope of your variables and avoid unintended modifications to the original data.

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