What is the library function for string comparison in the C language?

In the C language, the library function used to compare strings is `strcmp()`. It compares the contents of two strings and returns an integer value to indicate the result of the comparison.

The declaration of the `strcmp()` function is as follows:

int strcmp(const char *str1, const char *str2);

The function takes in two parameters of type `const char*`, which are the two strings to be compared.

The meaning of the return value of the function is as follows:

If `str1` is equal to `str2`, return 0.

If `str1` is less than `str2`, a negative number (usually -1) will be returned.

If `str1` is greater than `str2`, it will return a positive number (usually 1).

For example, the following code demonstrates how to compare two strings using the `strcmp()` function.

#include <stdio.h>
#include <string.h>
int main() {
   char str1[] = "Hello";
   char str2[] = "World";
   int result = strcmp(str1, str2);
   if (result == 0) {
       printf("The strings are equal\n");
   } else if (result < 0) {
       printf("%s is less than %s\n", str1, str2);
   } else {
       printf("%s is greater than %s\n", str1, str2);
   }
   return 0;
}

The output will be `Hello is less than World`, because the letter “H” has a lower value in the ASCII code than “W”.