Case Insensitive String Comparison in C

There is no function that does this in the C standard. Unix systems that comply with POSIX are required to have strcasecmp in the header strings.h; Microsoft systems have stricmp. To be on the portable side, write your own:

int strcicmp(char const *a, char const *b){    for (;; a++, b++) {        int d = tolower((unsigned char)*a) - tolower((unsigned char)*b);        if (d != 0 || !*a)            return d;    }}

But note that none of these solutions will work with UTF-8 strings, only ASCII ones.

Take a look at strcasecmp() in strings.h.

I've found built-in such method named from which contains additional string functions to the standard header .

Here's the relevant signatures :

int  strcasecmp(const char *, const char *);int  strncasecmp(const char *, const char *, size_t);

I also found it's synonym in xnu kernel (osfmk/device/subrs.c) and it's implemented in the following code, so you wouldn't expect to have any change of behavior in number compared to the original strcmp function.

tolower(unsigned char ch) {    if (ch >= 'A' && ch <= 'Z')        ch = 'a' + (ch - 'A');    return ch; }int strcasecmp(const char *s1, const char *s2) {    const unsigned char *us1 = (const u_char *)s1,                        *us2 = (const u_char *)s2;    while (tolower(*us1) == tolower(*us2++))        if (*us1++ == '\0')            return (0);    return (tolower(*us1) - tolower(*--us2));}