Use of strncmp function in C

strncmp() function

The strncmp function in C is used to compare a specified number of characters from the beginning of two strings. It is defined in the <string.h> header file.

Purpose:

• Partial String Comparison: strncmp is useful when only a portion of a string needs to be compared, rather than the entire string. This is particularly relevant when dealing with prefixes, command parsing, or verifying specific patterns at the start of a string.
• Bounded Comparison: It provides a safeguard against buffer overflows by limiting the number of characters compared.

How it works:
The function takes three arguments: two pointers to the strings to be compared (str1 and str2), and an integer n representing the maximum number of characters to compare. It compares characters lexicographically, one by one, from the beginning of each string until "mismatch is found".

Function Syntax

• int strncmp(const char *str1, const char *str2, size_t n);

Parameters:

• str1 → first string
• str2 → second string
• n → number of characters to compare

Return Value of function:

• Zero (0): If the first n characters of both strings are equal.
• Positive value: if first differing character in str1 is greater than that in str2 (difference ASCII value)
• Negative value: if first differing character in str1 is less than that in str2 (difference of ASCII value)

Example

#include <stdio.h>

#include <string.h>

int main() {

    char str1[] = "Computer";

    char str2[] = "Compute";

   

    // Compare first 7 characters

    int result = strncmp(str1, str2, 7);

    if (result == 0)

        printf("First 7 characters are same.\n");

    else if (result > 0)

        printf("str1 is greater than str2.\n");

    else

        printf("str1 is smaller than str2.\n");

    return 0;

}

Output of program:

First 7 characters are same.