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Hàm substr-count() trong PHP

Hướng dẫn cách sử dụng hàm substr-count() trong lập trình PHP

Tác dụng của hàm substr-count()

The substr_count() function counts the number of times a substring occurs in a string.

Please note that the substring search is performed in a case-sensitive manner.

The following table summarizes the technical details of this function.

Return Value: Returns the number of times the substring occurs in the string.
Changelog: Since PHP 7.1.0, the start and length parameters may now be a negative number. The length parameter may also be 0 now.
Version: PHP 4+

Syntax

The basic syntax of the substr_count() function is given with:

substr_count(string, substring, start, length);

The following example shows the substr_count() function in action.

<?php
// Sample strings
$str = "The woodpeckers live in the woods.";
$substr = "wood";

// Counting substring occurrences
echo substr_count($str, $substr);
?>

Parameters

The substr_count() function accepts the following parameters.

Parameter Description
string Required. Specifies the string to search in.
substring Required. Specifies the substring to search for.
start Optional. Specifies the position in the string from where the counting will start. If it is negative, counting will start from the end of the string.
length Optional. Specifies the maximum length (after the specified start) to search for the substring. A negative length counts from the end of string.

More Examples

Here're some more examples showing how substr_count() function actually works:

The following example demonstrates the usage of different parameters.

<?php
// Sample strings
$str = "The woodpeckers live in the woods.";
$substr = "wood";

// Getting the original length of the string
echo strlen($str)."<br>"; // Prints: 34

// The string is reduced to 'woodpeckers', so it prints 1
echo substr_count($str, $substr, 4, 11)."<br>";

// The string is reduced to 'the wood', so it prints 1
echo substr_count($str, $substr, -10, 9)."<br>";

// The string is reduced to 'live in', so it prints 0
echo substr_count($str, $substr, 16, 7);
?>

This function does not count overlapped substrings as you can see in the following example.

<?php
// Sample strings
$str = "abcabcabc";
$substr = "abcabc";

// Counting substring occurrences
echo substr_count($str, $substr); // Prints: 1 (not 2)
?>

If the sum of the start and the length parameter values is greater than the length of the string, this function generates a warning. Let's take a look at the following example:

<?php
// Sample strings
$str = "The woodpeckers live in the woods.";
$substr = "wood";

// Generates a warning because 10 + 30 > 34
echo substr_count($str, $substr, 10, 30);
?>

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