Comprehensive Guide to PHP strspn() Function with Practical Examples

Understanding the strspn() Function

PHP offers many string handling functions, among which strspn() calculates the length of the initial segment of a string consisting entirely of characters found in another string. This function helps quickly determine the number of shared characters at the start of two strings.

The basic syntax of strspn() is as follows:

int strspn(string $str1, string $str2 [, int $start [, int $length]])

Parameters explained:

str1: Required. The first string to examine.

str2: Required. The string containing characters to match.

start: Optional. The position in str1 to start examining from; defaults to 0.

length: Optional. The number of characters to examine; defaults to the length of str1.

The function returns the length of the initial segment of str1 consisting entirely of characters found in str2. If all characters in str1 are found in str2, it returns the length of str1.

Example Usage of strspn()

Here is an example showing how to use strspn() to count matching characters:

$str1 = "Hello, world!";
$str2 = "Hewoi";
$match = strspn($str1, $str2);
echo $match; // Outputs 2

In this example, the first two characters of $str1 ("H" and "e") are found in $str2, so the function returns 2.

Checking if All Characters Match

To check whether all characters in $str1 exist in $str2, use the following approach:

$str1 = "foobar";
$str2 = "oofrab";
if (strlen($str1) == strspn($str1, $str2)) {
    echo "$str1 contains only characters found in $str2";
} else {
    echo "$str1 contains characters not found in $str2";
}

This code compares the lengths and outputs whether all characters in $str1 are present in $str2.

Removing Non-Letter Characters Using substr() and strspn()

You can combine strspn() with substr() to remove all non-letter characters from a string, as shown here:

$str = "Hello, world!";
$letters_only = substr($str, strspn($str, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"));
echo $letters_only; // Outputs "Helloworld"

This method finds the position of the first non-letter character and extracts only the letters.

Using strspn() with Regular Expressions to Strip HTML Tags

Another use case is combining strspn() with regular expressions to strip HTML tags, keeping only the textual content:

$str = "<p>This is a <strong>text</strong> with <i>HTML</i> tags</p>";
$text_only = substr($str, strspn($str, " <>&abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"));
echo $text_only; // Outputs "This is a text with HTML tags"

This keeps common text characters and certain symbols while removing HTML tags.

Summary

The strspn() function is a powerful tool in PHP for string matching tasks. Understanding its parameters and usage allows for efficient string comparisons and filtering. When combined with substr() or regular expressions, it enhances string processing capabilities in everyday development.