strrpos
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String Functions
PHP Manual

# strspn

(PHP 4, PHP 5)

strspn — Finds the length of the initial segment of a string consisting entirely of characters contained within a given mask.

### Description

int strspn ( string `$subject` , string `$mask` [, int `$start` [, int `$length` ]] )

Finds the length of the initial segment of `subject` that contains only characters from `mask`.

If `start` and `length` are omitted, then all of `subject` will be examined. If they are included, then the effect will be the same as calling strspn(substr($subject, $start, $length), $mask) (see substr for more information).

The line of code:

`<?php
$var = strspn("42 is the answer to the 128th question.", "1234567890");
?>`
will assign 2 to $var, because the string "42" is the initial segment of `subject` that consists only of characters contained within "1234567890".

### Parameters

`subject`

  The string to examine.

`mask`

  The list of allowable characters.

`start`

  The position in `subject` to start searching.

  If `start` is given and is non-negative, then strspn() will begin examining `subject` at the `start`'th position. For instance, in the string 'abcdef', the character at position 0 is 'a', the character at position 2 is 'c', and so forth.

  If `start` is given and is negative, then strspn() will begin examining `subject` at the `start`'th position from the end of `subject`.

`length`

  The length of the segment from `subject` to examine.

  If `length` is given and is non-negative, then `subject` will be examined for `length` characters after the starting position.

  If `length`is given and is negative, then `subject` will be examined from the starting position up to `length` characters from the end of `subject`.

### Return Values

Returns the length of the initial segment of `subject` which consists entirely of characters in `mask`.

### Changelog

Version | Description
--- | ---
4.3.0 | The `start` and `length` parameters were added

### Examples

Example #1 strspn() example

`<?php
// subject does not start with any characters from mask
var_dump(strspn("foo", "o"));
// examine two characters from subject starting at offset 1
var_dump(strspn("foo", "o", 1, 2));
// examine one character from subject starting at offset 1
var_dump(strspn("foo", "o", 1, 1));
?>`

The above example will output:

    int(0)
    int(2)
    int(1)

### Notes

> Note: This function is binary-safe.

### See Also

- strcspn() - Find length of initial segment not matching mask

strrpos
strstr
String Functions
PHP Manual