strrpos

(PHP 4, PHP 5, PHP 7, PHP 8)

strrpos — 文字列中に、ある部分文字列が最後に現れる場所を探す

説明

strrpos(string $haystack, string $needle, int $offset = 0): int|false

文字列 haystack の中で、 needle が最後に現れる位置を探します。

パラメータ

haystack

検索対象の文字列。

needle

検索する文字列。

PHP 8.0.0 より前のバージョンでは、needle が文字列でない場合、数値に変換され、文字の通常の値として扱われていました。この振る舞いは PHP 7.3.0 以降では推奨されないので、この機能を使用しないことを強く推奨します。意図した動作に依存する場合、 needle を string に明示的にキャストするか、明示的に chr() 関数を呼び出すべきでしょう。

offset

ゼロまたは正の値の場合、 haystack の最初の offset バイトをスキップし、左から右に検索が行われます。

負の値の場合、 haystack の最初ではなく、最後から offset バイトの箇所より検索を開始します。検索は右から左に行われ、検索を開始した箇所から needle が最初に現れる場所を探します。

注意:
この方が、最後の offset バイト、またはそれより前にある最後の needle を効率的に探せます。

戻り値

needle が見つかった位置を、 haystack 文字列の先頭 (offset の値とは無関係) からの相対位置で返します。

注意: 文字列の開始位置は 0 であり、1 ではありません。

needle が見つからない場合は false を返します。

変更履歴

バージョン	説明
8.0.0	`needle` は、空文字列を受け入れるようになりました。
8.0.0	`needle` に数値を渡すことはサポートされなくなりました。
7.3.0	`needle` に数値を渡すことは非推奨になりました。

例

例1 needle が haystack の中にあるかどうかの確認

"位置 0 に文字が見つかった" と "文字が見つからなかった" 場合の戻り値は混同しやすいです。この違いを見分ける方法を以下に示します。

<?php

$pos = strrpos($mystring, "b");
if ($pos === false) { // 注意: 等号が 3 つ並んでいます
    // 見つからない...
}

?>

例2 オフセットつきの検索

<?php
$foo = "0123456789a123456789b123456789c";

// Looking for '0' from the 0th byte (from the beginning)
var_dump(strrpos($foo, '0', 0));

// Looking for '0' from the 1st byte (after byte "0")
var_dump(strrpos($foo, '0', 1));

// Looking for '7' from the 21th byte (after byte 20)
var_dump(strrpos($foo, '7', 20));

// Looking for '7' from the 29th byte (after byte 28)
var_dump(strrpos($foo, '7', 28));

// Looking for '7' right to left from the 5th byte from the end
var_dump(strrpos($foo, '7', -5));

// Looking for 'c' right to left from the 2nd byte from the end
var_dump(strrpos($foo, 'c', -2));

// Looking for '9c' right to left from the 2nd byte from the end
var_dump(strrpos($foo, '9c', -2));
?>

上の例の出力は以下となります。

int(0)
bool(false)
int(27)
bool(false)
int(17)
bool(false)
int(29)

参考

strpos() - 文字列内の部分文字列が最初に現れる場所を見つける
stripos() - 大文字小文字を区別せずに文字列が最初に現れる位置を探す
strripos() - 文字列中で、特定の(大文字小文字を区別しない)文字列が最後に現れた位置を探す
strrchr() - 文字列中に文字が最後に現れる場所を取得する
substr() - 文字列の一部分を返す

Found A Problem?

Learn How To Improve This Page • Submit a Pull Request • Report a Bug

＋add a note

User Contributed Notes 7 notes

down

brian at enchanter dot net ¶

17 years ago

The documentation for 'offset' is misleading.

It says, "offset may be specified to begin searching an arbitrary number of characters into the string. Negative values will stop searching at an arbitrary point prior to the end of the string."

This is confusing if you think of strrpos as starting at the end of the string and working backwards.

A better way to think of offset is:

- If offset is positive, then strrpos only operates on the part of the string from offset to the end. This will usually have the same results as not specifying an offset, unless the only occurences of needle are before offset (in which case specifying the offset won't find the needle).

- If offset is negative, then strrpos only operates on that many characters at the end of the string. If the needle is farther away from the end of the string, it won't be found.

If, for example, you want to find the last space in a string before the 50th character, you'll need to do something like this:

strrpos($text, " ", -(strlen($text) - 50));

If instead you used strrpos($text, " ", 50), then you would find the last space between the 50th character and the end of the string, which may not have been what you were intending.

down

dave at pixelmetrics dot com ¶

5 years ago

The description of offset is wrong. Here’s how it works, with supporting examples.

Offset effects both the starting point and stopping point of the search. The direction is always right to left. (The description wrongly says PHP searches left to right when offset is positive.)

Here’s how it works:
When offset is positive, PHP searches right to left from the end of haystack to offset. This ignores the left side of haystack.

When offset is negative, PHP searches right to left, starting offset bytes from the end, to the start of haystack. This ignores the right side of haystack.

Example 1:
$foo = ‘aaaaaaaaaa’;
var_dump(strrpos($foo, 'a', 5));
Result: int(10)

Example 2:
$foo = "aaaaaa67890";
var_dump(strrpos($foo, 'a', 5));
Result: int(5)

Conclusion: When offset is positive, PHP searches right to left from the end of haystack.

Example 3:
$foo = "aaaaa567890";
var_dump(strrpos($foo, 'a', 5));
Result: bool(false)

Conclusion: When offset is positive, PHP stops searching at offset.

Example 4:
$foo = ‘aaaaaaaaaa’;
var_dump(strrpos($foo, 'a', -5));
Result: int(6) 

Conclusion: When offset is negative, PHP searches right to left, starting offset bytes from the end. 

Example 5:
$foo = "a234567890";
var_dump(strrpos($foo, 'a', -5));
Result: int(0)

Conclusion: When offset is negative, PHP searches right to left, all the way to the start of haystack.

down

Daniel Brinca ¶

17 years ago

Here is a simple function to find the position of the next occurrence of needle in haystack, but searching backwards  (lastIndexOf type function):

//search backwards for needle in haystack, and return its position
function rstrpos ($haystack, $needle, $offset){
    $size = strlen ($haystack);
    $pos = strpos (strrev($haystack), $needle, $size - $offset);
    
    if ($pos === false)
        return false;
    
    return $size - $pos;
}

Note: supports full strings as needle

down

david dot mann at djmann dot co dot uk ¶

6 years ago

Ten years on, Brian's note is still a good overview of how offsets work, but a shorter and simpler summary is:

    strrpos($x, $y, 50);  // 1: this tells strrpos() when to STOP, counting from the START of $x
    strrpos($x, $y, -50); // 2: this tells strrpos() when to START, counting from the END of $x

Or to put it another way, a positive number lets you search the rightmost section of the string, while a negative number lets you search the leftmost section of the string.

Both these variations are useful, but picking the wrong one can cause some highly confusing results!

down

-3

ZaraWebFX ¶

21 years ago

this could be, what derek mentioned:

<?
function cut_last_occurence($string,$cut_off) {
    return strrev(substr(strstr(strrev($string), strrev($cut_off)),strlen($cut_off)));
}    

//    example: cut off the last occurence of "limit"
    $str = "select delta_limit1, delta_limit2, delta_limit3 from table limit 1,7";
    $search = " limit";
    echo $str."\n";
    echo cut_last_occurence($str,"limit");
?>

down

-4

php NO at SPAMMERS willfris SREMMAPS dot ON nl ¶

18 years ago

<?php
/*******
 ** Maybe the shortest code to find the last occurence of a string, even in php4
 *******/
function stringrpos($haystack,$needle,$offset=NULL)
{
    return strlen($haystack)
           - strpos( strrev($haystack) , strrev($needle) , $offset)
           - strlen($needle);
}
// @return   ->   chopped up for readability.
?>

down

-4

genetically altered mastermind at gmail ¶

19 years ago

Very handy to get a file extension:
$this->data['extension'] = substr($this->data['name'],strrpos($this->data['name'],'.')+1);

＋add a note