Using PHP strpos() to Find Character and Substring Positions

In PHP, string handling often requires locating the position of a specific character or substring. The built‑in function strpos() is used for this purpose.

1. Basic usage of strpos()

The function returns the position of the first occurrence of the needle in the haystack, or false if not found. Its syntax is:

int strpos ( string $haystack , mixed $needle [, int $offset = 0 ] )

$haystack is the target string, $needle is the character or substring to search for, and $offset (optional) specifies the starting index for the search.

2. Example: Find the character 'o'

Assume the following string:

$str = "Hello, world!";

To find the position of the character 'o' :

$pos = strpos($str, 'o');
if ($pos === false) {
    echo "未找到字符'o'";
} else {
    echo "字符'o'在位置：" . $pos;
}

The code searches for the first occurrence of 'o' and outputs its index (0‑based). The result is 4 .

3. Example: Find a substring

To locate the substring 'wor' within the same string:

$sub_str = 'wor';
$pos = strpos($str, $sub_str);
if ($pos === false) {
    echo "未找到字符串'$sub_str'";
} else {
    echo "字符串'$sub_str'在位置：" . $pos;
}

This returns position 7 , the index of the first character of the substring.

4. Example: Search with an offset

When you need to start searching from a specific index, provide the $offset parameter:

$sub_str = 'o';
$pos = strpos($str, $sub_str, 5);
if ($pos === false) {
    echo "未找到字符'$sub_str'";
} else {
    echo "字符'$sub_str'在位置：" . $pos;
}

With an offset of 5 , the function finds the next 'o' at index 8 .

Summary

The article introduces the PHP strpos() function, explains its parameters, and provides multiple code examples showing how to locate characters, substrings, and how to use the optional offset argument. Mastering this function simplifies many string‑processing tasks in backend development.