strrpos

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

strrpos — Trova la posizione dell'ultima occorrenza di un carattere in una stringa

Descrizione

strrpos(string $haystack, string $needle, int $offset = ?): int

Restituisce la posizione numerica dell'ultima occorrenza di needle nella stringa haystack. Fare attenzione che needle, in PHP 4, può essere solo un singolo carattere. Se si passa una stringa, verrà utilizzato solo il primo carattere.

Se needle non viene trovato, la funzione restituisce false.

Si può facilmente confondere i valori restituiti "per carattere alla posizione 0" e per "carattere non trovato". Ecco come rilevare la differenza:

<?php

// in PHP 4.0b3 e successivi:
$pos = strrpos($mystring, "b");
if ($pos === false) { // note: three equal signs
    // not found...
}

// nelle versioni precedenti alla 4.0b3:
$pos = strrpos($mystring, "b");
if (is_bool($pos) && !$pos) {
    // not found...
}
?>

Se needle non è una stringa, viene convertito in un intero, e usato come valore ordinale di un carattere.

Nota: Dal PHP 5.0.0 offset può essere indicato per indicare di iniziare la ricerca nella stringa da una posizione di caratteri arbitraria. Valori negativi fermeranno la ricerca ad un punto arbitrario prima della fine della stringa.

Nota: Il parametro needle può essere una stringa di uno o più caratteri a partire dal PHP 5.0.0.

Vedere anche: strpos(), strripos(), strrchr(), substr(), stristr() e strstr().

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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

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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);

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