How to use php strncmp() function

In the PHP programming language, many string comparison functions are provided to compare whether two strings are equal and perform some further operations. One of the commonly used string comparison functions is the strncmp function. This function compares the first n characters of two strings to see if they are equal. In this article, we will introduce the usage of strncmp function and its practical application in PHP programming.

1. Grammar

The syntax of the strncmp function is as follows:

int strncmp ( string $str1 , string $str2 , int $n )

Among them, str1 and str2 are the two strings to be compared, and n refers to The number of characters to compare.

2. Return value

This function will return one of the following values:

• If str1 is less than str2, a negative integer will be returned.
• If str1 is equal to str2, 0 will be returned.
• If str1 is greater than str2, a positive integer will be returned.

3. Example

The following is a simple PHP program to illustrate the use of strncmp function:

<?php
$str1 = "apple";
$str2 = "apricot";
$n = 3;
$result = strncmp($str1, $str2, $n);
if ($result < 0){
    echo "The first 3 characters of str1 are less than the first 3 characters of str2";
}elseif ($result == 0){
    echo "The first 3 characters of str1 are equal to the first 3 characters of str2";
}else{
    echo "The first 3 characters of str1 are greater than the first 3 characters of str2";
}
?>

The above code running results are as follows :

The first 3 characters of str1 are less than the first 3 characters of str2

4. Practical application

In practical applications, the strncmp function is mainly used in the following two situations:

• Compare two characters Whether the strings are equal

You can use the strncmp function to compare whether the first characters of the two strings are equal. If they are equal, continue to compare the following characters; if they are not equal, you can draw the conclusion that the two strings are equal. The strings are not equal.

The following is a sample program for comparing whether two strings are equal:

<?php
$str1 = "hello world";
$str2 = "hello";
$n = strlen($str2);
$result = strncmp($str1, $str2, $n);
if ($result == 0){
    echo "The two strings are equal";
}else{
    echo "The two strings are not equal";
}
?>

The results of the above code are as follows:

The two strings are equal

• Compare whether the file contents are equal

In PHP programming, you can also use the strncmp function to compare whether the contents of two files are equal. Below is a sample program that compares the contents of two files for equality:

<?php
$file1 = "file1.txt";
$file2 = "file2.txt";
$n = 100;
$f1 = fopen($file1, "r");
$f2 = fopen($file2, "r");
$str1 = fread($f1, $n);
$str2 = fread($f2, $n);
$result = strncmp($str1, $str2, $n);
if ($result == 0){
    echo "The contents of the two files are equal";
}else{
    echo "The contents of the two files are not equal";
}
fclose($f1);
fclose($f2);
?>

The results of running the above code will vary depending on the contents of the two files.

5. Summary

This article introduces the syntax and usage of strncmp function, and explains its practical application in PHP programming. I hope this article can inspire some work related to string comparison in PHP programming and improve the work efficiency of programmers.

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