NAME

strcasecmp - compare two strings ignoring case

strcasecmp, strncasecmp - compare two strings ignoring case

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

Header Files

#include <cs50.h>
#include <strings.h>

Prototype

int strcasecmp(string s1, string s2);

#include <strings.h>
int strcasecmp(const char *s1, const char *s2);
int strncasecmp(const char s1[.n], const char s2[.n], size_t n);

DESCRIPTION

This function compares two strings case-insensitively.

The strcasecmp() function performs a byte-by-byte comparison of the strings s1 and s2, ignoring the case of the characters. It returns an integer less than, equal to, or greater than zero if s1 is found, respectively, to be less than, to match, or be greater than s2.

The strncasecmp() function is similar, except that it compares no more than n bytes of s1 and s2.

RETURN VALUE

This function returns

an int less than 0 if s1 comes before s2, ignoring case,
0 if s1 is the same as s2, ignoring case, or
an int greater than 0 if s1 comes after s2, ignoring case.

The strings are compared using “ASCIIbetical” order, based on the ASCII values of their characters. For instance, "AAA" would come before "BBB".

The strcasecmp() and strncasecmp() functions return an integer less than, equal to, or greater than zero if s1 is, after ignoring case, found to be less than, to match, or be greater than s2, respectively.

EXAMPLE

#include <cs50.h>
#include <stdio.h>
#include <strings.h>

int main(void)
{
    string s1 = get_string("s1: ");
    string s2 = get_string("s2: ");
    if (strcasecmp(s1, s2) == 0)
    {
        printf("Those are the same, ignoring case.\n");
    }
    else
    {
        printf("Those are different, even ignoring case.\n");
    }
}

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface	Attribute	Value
strcasecmp(), strncasecmp()	Thread safety	MT-Safe locale

STANDARDS

POSIX.1-2008.

HISTORY

4.4BSD, POSIX.1-2001.

The strcasecmp() and strncasecmp() functions first appeared in 4.4BSD, where they were declared in <string.h>. Thus, for reasons of historical compatibility, the glibc <string.h> header file also declares these functions, if the _DEFAULT_SOURCE (or, in glibc 2.19 and earlier, _BSD_SOURCE) feature test macro is defined.

The POSIX.1-2008 standard says of these functions:

When the LC_CTYPE category of the locale being used is from the POSIX locale, these functions shall behave as if the strings had been converted to lowercase and then a byte comparison performed. Otherwise, the results are unspecified.