w3resource

PHP: strspn() function

Description

The strspn() function is used to find the length of the initial segment of a string which matches characters from a second string.

Version:

(PHP 4 and above)

Syntax:

strspn(main_string, search_string, start_position, length) 

Parameters:

Name Description Required /
Optional
Type
main_string The first string. Required String
search_string The searched string. Required String
start_position Sets the starting position of the first string. Negative value counts position from the end of main_string. Optional Integer
length Sets the no. of characters to be checked in the main_string. Optional Integer

Return value:

Returns the length of the initial segment of main_string.

Value Type: Integer

Pictorial Presentation

string_strspn

Example:

<?php
$string1='W3RESOURCE';
echo strspn($string1, 'W3Res');
?>

Output:

3

View the example in the browser

See also

PHP Function Reference

Previous: strrpos
Next: strstr



PHP: Tips of the Day

PHP - How do I implement a callback in PHP?

The manual uses the terms "callback" and "callable" interchangeably, however, "callback" traditionally refers to a string or array value that acts like a function pointer, referencing a function or class method for future invocation. This has allowed some elements of functional programming since PHP 4. The flavors are:

$cb1 = 'someGlobalFunction';
$cb2 = ['ClassName', 'someStaticMethod'];
$cb3 = [$object, 'somePublicMethod'];

// this syntax is callable since PHP 5.2.3 but a string containing it
// cannot be called directly
$cb2 = 'ClassName::someStaticMethod';
$cb2(); // fatal error

// legacy syntax for PHP 4
$cb3 = array(&$object, 'somePublicMethod');

This is a safe way to use callable values in general:

if (is_callable($cb2)) {
    // Autoloading will be invoked to load the class "ClassName" if it's not
    // yet defined, and PHP will check that the class has a method
    // "someStaticMethod". Note that is_callable() will NOT verify that the
    // method can safely be executed in static context.

    $returnValue = call_user_func($cb2, $arg1, $arg2);
}

Modern PHP versions allow the first three formats above to be invoked directly as $cb(). call_user_func and call_user_func_array support all the above.

Notes/Caveats:

  1. If the function/class is namespaced, the string must contain the fully-qualified name. E.g. ['Vendor\Package\Foo', 'method']
  2. call_user_func does not support passing non-objects by reference, so you can either use call_user_func_array or, in later PHP versions, save the callback to a var and use the direct syntax: $cb();
  3. Objects with an __invoke() method (including anonymous functions) fall under the category "callable" and can be used the same way, but I personally don't associate these with the legacy "callback" term.
  4. The legacy create_function() creates a global function and returns its name. It's a wrapper for eval() and anonymous functions should be used instead.

Ref : https://bit.ly/2Zmqil0