What Does the strcmp Return Value Mean? Understanding 0, Positive, and Negative Results

gitbox 2025-08-13

In PHP, strcmp() is a commonly used string comparison function. It compares the size of two strings and returns different values based on the comparison. Understanding the meaning of strcmp() return values is very important when handling string operations in development.

Basic Syntax of strcmp() Function

The syntax of strcmp() is as follows:

<span><span><span class="hljs-keyword">int</span></span><span> </span><span><span class="hljs-title function_ invoke__">strcmp</span></span><span>(</span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$str1</span></span><span> , </span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$str2</span></span><span> )</span></span>

This function takes two parameters, str1 and str2, and returns an integer representing the comparison result between the two strings.

Meaning of Return Values

The integer returned by strcmp() usually has three possible outcomes: negative, zero, or positive.

1. When 0 is returned

When strcmp() returns 0, it means the two strings are exactly equal, including their content, case, and length. In short, the strings are identical in every way.

<span><span><span class="hljs-variable">$str1</span></span><span> = </span><span><span class="hljs-string">"hello"</span></span>;
</span><span><span class="hljs-variable">$str2</span></span><span> = </span><span><span class="hljs-string">"hello"</span></span>;
<p></span>if(strcmp($str1, $str2) == 0) {<br>
</span>echo </span>"The two strings are equal";<br>
}<br>
</span></span>

2. When a negative value is returned

When strcmp() returns a negative value, it indicates that str1 is less than str2. This comparison is based on the ASCII values of characters. In other words, if str1 comes before str2 in dictionary order, the return value will be negative.

For example, comparing "apple" with "banana" returns a negative value because the ASCII value of a is less than that of b.

<span><span><span class="hljs-variable">$str1</span></span><span> = </span><span><span class="hljs-string">"apple"</span></span>;
</span><span><span class="hljs-variable">$str2</span></span><span> = </span><span><span class="hljs-string">"banana"</span></span>;
<p></span>if(strcmp($str1, $str2) < 0) {<br>
</span>echo </span>"'apple' is less than 'banana'";<br>
}<br>
</span></span>

3. When a positive value is returned

When strcmp() returns a positive value, it indicates that str1 is greater than str2. That is, str1 comes after str2 in dictionary order.

For example, comparing "banana" with "apple" returns a positive value because the ASCII value of b is greater than a.

<span><span><span class="hljs-variable">$str1</span></span><span> = </span><span><span class="hljs-string">"banana"</span></span>;
</span><span><span class="hljs-variable">$str2</span></span><span> = </span><span><span class="hljs-string">"apple"</span></span>;
<p></span>if(strcmp($str1, $str2) > 0) {<br>
</span>echo </span>"'banana' is greater than 'apple'";<br>
}<br>
</span></span>

String Comparison is Case-Sensitive

It is important to note that strcmp() comparisons are case-sensitive. If you want a case-insensitive comparison, you can use functions like strcoll() or strcasecmp().

<span><span><span class="hljs-variable">$str1</span></span><span> = </span><span><span class="hljs-string">"Hello"</span></span>;
</span><span><span class="hljs-variable">$str2</span></span><span> = </span><span><span class="hljs-string">"hello"</span></span>;
<p></span>if(strcmp($str1, $str2) != 0) {<br>
</span>echo </span>"The strings are different";<br>
}<br>
</span></span>

In this example, strcmp() will return a non-zero value because the ASCII value of 'H' is different from 'h'.

Conclusion

strcmp() is a powerful string comparison function that helps us understand the relative order of two strings by returning negative, zero, or positive values:

Returns 0: The two strings are equal.
Returns a negative value: str1 is less than str2.
Returns a positive value: str1 is greater than str2.

Understanding the return values of this function is very helpful for optimizing and debugging string operations.

strcmp