Applies the user-defined function func to each element of the array array. Typically, func takes on two parameters. The array parameter's value being the first, and the key/index second. If the optional userdata parameter is supplied, it will be passed as the third parameter to function func.
func must be a user-defined function, not a built-in PHP function such as strtolower() or stripslashes(). The user-defined function can use built-in PHP functions.
Note: Instead of a function name, an array containing an object reference and a method name can also be supplied.
If function func requires more parameters than given to it, an error of level E_WARNING will be generated each time array_walk() calls func. These warnings may be suppressed by prepending the PHP error operator @ to the array_walk() call, or by using error_reporting().
Note: If func needs to be working with the actual values of the array, specify the first parameter of func as a reference. Then, any changes made to those elements will be made in the original array itself.
Note: Passing the key and userdata to func was added in 4.0.0
array_walk() is not affected by the internal array pointer of array. array_walk() will walk through the entire array regardless of pointer position. To reset the pointer, use reset(). In PHP 3, array_walk() resets the pointer.
Users may not change the array itself from the callback function. e.g. Add/delete elements, unset elements, etc. If the array that array_walk() is applied to is changed, the behavior of this function is undefined, and unpredictable.
See also list(), foreach, each(), and call_user_func_array().