The strcoll function is used to compare two strings based on the current locale. It is declared in the string.h header file and has the following prototype:

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

The str1 and str2 arguments are pointers to the null-terminated strings to be compared. The function returns an integer value that indicates the relationship between the two strings. The value returned by strcoll is dependent on the locale, but it can be thought of as being similar to the value returned by strcmp.

The strcoll function performs a "collating sequence" comparison of the two strings. This means that it takes into account the way that characters are ordered in the current locale. For example, in some locales, the character 'a' might come before 'b', while in others, 'a' might come after 'b'. The strcoll function uses this ordering to determine the relationship between the two strings.

Note that strcoll only compares strings for equality, less than, or greater than; it does not return the difference between the strings. If you need to compute the difference between two strings, you can use the strcmp function.