strrpos

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

strrpos — Find the position of the last occurrence of a substring in a string

Опис

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

Find the numeric position of the last occurrence of needle in the haystack string.

Параметри

haystack

The string to search in.

needle

The string to search for.

До версії PHP 8.0.0, якщо параметр needle не є рядком, він перетворюється на ціле число і розглядається як код символу. Ця поведінка є застарілою, починаючи з PHP 7.3.0. Вкрай не рекомендується на неї покладатися. Залежно від потрібної поведінки, параметр needle необхідно привести до рядкового типу або обробити функцією chr().

offset

If zero or positive, the search is performed left to right skipping the first offset bytes of the haystack.

If negative, the search starts offset bytes from the right instead of from the beginning of haystack. The search is performed right to left, searching for the first occurrence of needle from the selected byte.

Зауваження:
This is effectively looking for the last occurrence of needle at or before the last offset bytes.

Значення, що повертаються

Returns the position where the needle exists relative to the beginning of the haystack string (independent of search direction or offset).

Зауваження: String positions start at 0, and not 1.

Returns false if the needle was not found.

Увага

Ця функція може повертати як логічне false, так і не логічне значення, яке прирівнюється до false. Докладніше про це описано в розділі Логічні типи даних. Для перевірки значення, яке повертає ця функція, використовується оператор ===.

Помилки/виключення

If offset is greater than the length of haystack, a ValueError will be thrown.

Журнал змін

Версія	Опис
8.0.0	Тепер параметр `needle` може бути порожнім рядком.
8.0.0	Passing an int as `needle` is no longer supported.
7.3.0	Passing an int as `needle` has been deprecated.

Приклади

Приклад #1 Checking if a needle is in the haystack

It is easy to mistake the return values for "character found at position 0" and "character not found". Here's how to detect the difference:

<?php
$mystring = 'Elephpant';

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

?>

Приклад #2 Searching with offsets

<?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));
?>

Поданий вище приклад виведе:

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

Прогляньте також

strpos() - Знаходить позицію першого входження підрядка в рядку
stripos() - Find the position of the first occurrence of a case-insensitive substring in a string
strripos() - Find the position of the last occurrence of a case-insensitive substring in a string
strrchr() - Find the last occurrence of a character in a string
substr() - Return part of a string

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User Contributed Notes 5 notes

down

brian at enchanter dot net ¶

18 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 ¶

6 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 ¶

18 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 ¶

7 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

biziclop at example dot net ¶

2 hours ago

An example function to show how to iterate through all matches in reverse order:  
<?php

function str_positions_reverse( $haystack, $needle, $fn = null ){
  if( $fn === null )  $positions = array();
  $needlen = strlen( $needle );
  $offset  = strlen( $haystack ) + $needlen;
  $pos     = strrpos( $haystack, $needle );
  while( $pos !== false ){
    if( $fn === null )  $positions[] = $pos;
    else if( null !== ( $r = $fn( $pos, $haystack, $needle )))  return $r;
    if( $pos < $needlen )  break;
    $pos = strrpos( $haystack, $needle, $pos - $offset );
  }
  if( $fn === null )  return $positions;
}

echo implode(',', str_positions_reverse('111111',  '11'));  // 4,2,0
echo implode(',', str_positions_reverse('1111111', '11'));  // 5,3,1

$path = '/Users//'.get_current_user().'/./Desktop/path/to/a/file.txt';
echo $path; // /Users//alfred.e.neumann/./Desktop/path/to/a/file.txt

echo 'slashes: ', implode(',', str_positions_reverse( $path, '/'));
// slashes: 44,42,39,34,26,24,7,6,0

echo "\nclosest real file: ", str_positions_reverse( $path, '/', function( $pos, $path ){
  $path = realpath( substr( $path, 0, $pos ));
  if( $path !== false )  return $path;
});
// closest real file: /Users/alfred.e.neumann/Desktop
?>

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