The most direct way to find the last occurrence of a substring in PHP is to use the strrpos() function. 1. Use the strrpos() function to directly obtain the index of the last occurrence of the substring in the main string. If it is not found, it returns false. The syntax is strrpos($haystack, $needle, $offset = 0). 2. If you need to ignore case, you can use the strripos() function to implement case-insensitive searches. 3. For multi-byte characters such as Chinese, the mb_strrpos() function in the mbstring extension should be used to ensure that the character position is returned instead of the byte position. 4. Note that when strrpos() returns false, you need to use the !== operator to judge to avoid logical errors; at the same time, you can specify the search starting position through the $offset parameter according to your needs.

The most direct way to find the last occurrence of a substring in PHP is to use strrpos() function. It returns the start position where the substring last appears in the main string, and false if it is not found.

1. Use strrpos() to find the last location

This is the most commonly used and recommended method. The syntax is as follows:

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

• $haystack is the main string.
• $needle is the substring you are looking for.
• $offset (optional) indicates where to start the search.

Example:

 $str = "Hello world, welcome to the world of PHP.";
$pos = strpos($str, "world");

if ($pos !== false) {
    echo "The last location that appears is: $pos";
} else {
    echo "Substring not found";
}

The output result is:

 The last location is: 27

Note that the position index where the first character matches is returned here, not bytes or characters.

2. Case sensitivity issues

strrpos() is case sensitive. If you need to lookup insensitively, you can use the strripos() function, which is used similarly to strrpos() , but ignores case.

 $pos = strripos("Hello World", "world"); // Return 6

This function is very useful when processing user input or data in uncertain case format.

3. Handle multi-byte characters such as Chinese

If you are dealing with Chinese or other non-ASCII characters, using strrpos() directly may result in wrong results because it calculates position by bytes. At this time, you should use the mb_strrpos() function in mbstring extension:

 $pos = mb_strrpos("Hello, world! Welcome to the world.", "world");

It returns character positions rather than byte positions, which are more suitable for multilingual text.

Make sure that mbstring extension is enabled in your environment.

4. Common Errors and Precautions

• The return value is false : When no substring is found, strrpos() returns a boolean value false , not -1 or other numerical value, so use !== false to judge.

• Do not use == to compare the results : For example, $pos == false will also treat the position 0 as false, resulting in a logical error.

• Use of offset : The third parameter $offset is to search from the first character of the main string. For example:

   strrpos("abcdefabc", "abc", 3); // Start searching after the third character, the result is 6

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  Basically that's it. PHP provides a variety of ways to locate the last occurrence position of the substring, and select the appropriate function according to the actual scene.

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