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array_walk - Apply a user supplied function to every member of an array
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array_walk( array|objectarray, callable$callback, [mixed$arg = null] ): bool

Applies the user-defined callback function to each element of the array array.

array_walk is not affected by the internal array pointer of array. array_walk will walk through the entire array regardless of pointer position.



The input array.


Typically, callback takes on two parameters. The array parameter's value being the first, and the key/index second.


If callback needs to be working with the actual values of the array, specify the first parameter of callback as a reference. Then, any changes made to those elements will be made in the original array itself.


Many internal functions (for example strtolower) will throw a warning if more than the expected number of argument are passed in and are not usable directly as a callback.

Only the values of the array may potentially be changed; its structure cannot be altered, i.e., the programmer cannot add, unset or reorder elements. If the callback does not respect this requirement, the behavior of this function is undefined, and unpredictable.


If the optional arg parameter is supplied, it will be passed as the third parameter to the callback.

Return Values

Returns true.

Exceptions and Errors

As of PHP 7.1.0, an ArgumentCountError will be thrown if the callback function requires more than 2 parameters (the value and key of the array member), or more than 3 parameters if the arg is also passed. Previously, in this case an error of level E_WARNING would be generated each time array_walk calls callback.


Version Description
8.0.0 If callback expects the second or third parameter to be passed by reference, this function will now emit an E_WARNING.

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