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
Example:
<?php
$string1='W3RESOURCE';
echo strspn($string1, 'W3Res');
?>
Output:
3
View the example in the browser
See also
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:
- If the function/class is namespaced, the string must contain the fully-qualified name. E.g. ['Vendor\Package\Foo', 'method']
- 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();
- 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.
- 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
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