How does PHP calculate the last occurrence of a specified string in the target string (case-insensitive)

How does PHP calculate the position of the last occurrence of a specified string in the target string (case-insensitive)? This is a problem that many PHP developers often encounter when processing strings. This article will demonstrate how to use PHP built-in functions to implement this function through example code to help readers better understand and use it. Let us follow the guidance of PHP editor Xiaoxin and explore how to implement this technique.

The last occurrence position of a case-insensitive string in PHP

introduction

In php, calculating the position of the last occurrence of a specified string in the target string (case-insensitive) is a common task in text processing. This article will introduce in detail how to use PHP's built-in functions and regular expressions to achieve this function.

Use built-in functions strrpos()

strrpos() The function can be used to find the last occurrence of a specified substring in a string, case-insensitively. Its syntax is as follows:

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

in:

• $haystack: target string
• $needle: Substring to find
• $offset: Optional offset, specifying the position in the string to start searching (default is 0)

If the substring is found, this function returns the position of its last occurrence; otherwise, -1 is returned.

Example:

$haystack = "Hello, world! Hello, PHP!";
$needle = "hello";
$result = strrpos($haystack, $needle, 10); // Start searching at offset 10
if ($result !== -1) {
echo "The last occurrence of the substring: $result";
}

Output:

The last occurrence of the substring: 21

Use regular expressions

Regular expression is a powerful pattern matching tool, which can also be used to find the last occurrence of a substring in a string. The regular expression pattern .*? can be used to match any sequence of leading characters until a substring is found.

Example:

$haystack = "Hello, world! Hello, PHP!";
$needle = "hello";
$pattern = "/.*?{$needle}/i"; // Use case-insensitive flag i
$result = preg_match($pattern, $haystack, $matches);
if ($result) {
echo "The last occurrence of the substring:".strlen($matches[0]) - strlen($needle);
}

Output:

The last occurrence of the substring: 21

Summarize

PHP provides multiple methods to calculate the position of the last occurrence of a specified string in the target string, case-insensitively. The built-in function strrpos() can quickly and easily find the last occurrence of a substring, while regular expressions provide more flexible options. Depending on the specific requirements of your application, choosing the appropriate method can improve the efficiency and accuracy of your code.

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