PHP Basics

How To Compare Strings In PHP

During any sort of programming you will always get situations where you need to compare values with each other, if the values are boolean or integers then the comparison is simple. But if you want to compare strings or parts of strings then there can be more to the comparison such as case of the string you are comparing.

In this tutorial we are going to look at all the different ways you can compare strings in PHP using a number of built in PHP functions.

== operator

The most common way you will see of comparing two strings is simply by using the == operator if the two strings are equal to each other then it returns true.

// Using the == operator, Strings match is printed
if('string1' == 'string1')
{
    echo 'Strings match.';
} else {
    echo 'Strings do not match.';
}

This code will return that the strings match, but what if the strings were not in the same case it will not match. If all the letters in one string were in uppercase then this will return false and that the strings do not match.

// Using the == operator, Strings do not match is printed
if('string1' == 'STRING1')
{
    echo 'Strings match.';
} else {
    echo 'Strings do not match.';
}

This means that we can't use the == operator when comparing strings from user inputs, even if the first letter is in uppercase it will still return false. So we need to use some other function to help compare the strings.

strcmp Function

Another way to compare strings is to use the PHP function strcmp, this is a binary safe string comparison function that will return a 0 if the strings match.

// strcmp function, Strings match is printed
if(strcmp('string1', 'string1') == 0)
{
     echo 'Strings match.';
} else {
     echo 'Strings do not match.';
}

This if statement will return true and echo that the strings match. But this function is case sensitive so if one of the strings has an uppercase letter then the function will not return 0.

strcasecmp Function

The previous examples will not allow you to compare different case strings, the following function will allow you to compare case insensitive strings.

// Both strings will match
if(strcasecmp('string1', 'string1') == 0)
{
     echo 'Strings match.';
} else {
     echo 'Strings do not match.';
}
 
// Both strings will match even with different case
if(strcasecmp('string1', 'String1') == 0)
{
     echo 'Strings match.';
} else {
     echo 'Strings do not match.';
}
 
// Both strings will match even with different case
if(strcasecmp('string1', 'STRING1') == 0)
{
     echo 'Strings match.';
} else {
     echo 'Strings do not match.';
}

All of these if statements will return that the strings match, which means that we can use this function when comparing strings that are input by the user.

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Comments

  1. Frank says:

    You may want to talk about the danger of using == instead of === when comparing strings. See http://stackoverflow.com/questions/3333353/string-comparison-using-vs-strcmp