String comparison functions in PHP

Introduction

String comparison functions help you check if two pieces of text are the same or which one comes first in order. This is useful when sorting or checking user input.

Checking if a username entered matches a stored username.

Sorting a list of words alphabetically.

Comparing passwords or codes for equality.

Finding if one string appears before another in dictionary order.

Validating form inputs against expected values.

Syntax

PHP

strcmp(string $str1, string $str2): int
strcasecmp(string $str1, string $str2): int
strncmp(string $str1, string $str2, int $length): int
strncasecmp(string $str1, string $str2, int $length): int

These functions return 0 if the strings are equal.

A negative number means the first string is less than the second; a positive means it is greater.

Examples

Compare two strings exactly, case-sensitive.

PHP

$result = strcmp("apple", "banana");
// $result will be negative because "apple" comes before "banana"

Compare two strings ignoring uppercase or lowercase differences.

PHP

$result = strcasecmp("Apple", "apple");
// $result will be 0 because comparison ignores case

Compare only the first few characters of two strings.

PHP

$result = strncmp("applepie", "applesauce", 5);
// Compares only first 5 characters

Compare first few characters ignoring case.

PHP

$result = strncasecmp("ApplePie", "appleSauce", 5);
// Case-insensitive comparison of first 5 characters

Sample Program

This program compares strings using different functions and prints what it finds. It shows case-sensitive and case-insensitive comparisons, and compares full strings or just the first few characters.

PHP

<?php

// Compare two strings case-sensitive
$result1 = strcmp("hello", "Hello");

// Compare two strings ignoring case
$result2 = strcasecmp("hello", "Hello");

// Compare first 3 characters case-sensitive
$result3 = strncmp("hello", "helium", 3);

// Compare first 3 characters ignoring case
$result4 = strncasecmp("Hello", "heLium", 3);

// Print results
if ($result1 === 0) {
    echo "strcmp: Strings are equal\n";
} elseif ($result1 < 0) {
    echo "strcmp: 'hello' is less than 'Hello'\n";
} else {
    echo "strcmp: 'hello' is greater than 'Hello'\n";
}

if ($result2 === 0) {
    echo "strcasecmp: Strings are equal ignoring case\n";
}

if ($result3 === 0) {
    echo "strncmp: First 3 characters are equal\n";
} else {
    echo "strncmp: First 3 characters are different\n";
}

if ($result4 === 0) {
    echo "strncasecmp: First 3 characters are equal ignoring case\n";
} else {
    echo "strncasecmp: First 3 characters are different ignoring case\n";
}

Important Notes

Remember that strcmp and strncmp are case-sensitive.

Use strcasecmp and strncasecmp when you want to ignore letter case.

These functions return an integer, not a boolean true/false.

Summary

String comparison functions check if texts are equal or which comes first.

Use strcmp and strncmp for case-sensitive checks.

Use strcasecmp and strncasecmp to ignore case differences.