C String stricmp() Function

What You’ll Learn

The stricmp() function compares two C-strings without regard to letter case. It is the Microsoft/Windows-style companion to POSIX strcasecmp()—ideal for matching user commands like quit and QUIT.

Definition and Usage

stricmp performs a case-insensitive lexicographic comparison of two strings. It walks both strings in parallel, folding ASCII letters before comparing bytes, and stops at the first difference or at the shared null terminator.

The function is not part of standard C. Microsoft documents _stricmp; many Windows programs still say stricmp. On Linux and macOS, use strcasecmp from <strings.h> instead.

📝 Syntax

Typical Microsoft-style declaration:

int stricmp(const char *s1, const char *s2);
/* MSVC documented form: */
int _stricmp(const char *s1, const char *s2);

Headers and Portability

• Windows (MSVC, MinGW) — #include <string.h>
• Linux / macOS — use strcasecmp() in <strings.h>
• Related — _strnicmp / bounded compare (Windows)

Return Value

• 0 — strings equal ignoring case.
• < 0 — s1 less than s2 (case-insensitive order).
• > 0 — s1 greater than s2.

Examples Gallery

Examples target Windows/MSVC with <string.h>. On Linux or macOS, replace stricmp with strcasecmp and include <strings.h>.

#include <stdio.h>
#include <string.h>

int main(void) {
    const char *s1 = "Hello, World!";
    const char *s2 = "hello, world!";

    int result = _stricmp(s1, s2);

    if (result == 0) {
        printf("The strings are equal (ignoring case).\n");
    } else if (result < 0) {
        printf("s1 is less than s2.\n");
    } else {
        printf("s1 is greater than s2.\n");
    }

    return 0;
}

The strings are equal (ignoring case).

#include <stdio.h>
#include <string.h>

int main(void) {
    const char *a = "Hello";
    const char *b = "Help";

    if (_stricmp(a, b) == 0) {
        printf("Match\n");
    } else {
        printf("No match (letters differ at 'l' vs 'p').\n");
    }

    return 0;
}

No match (letters differ at 'l' vs 'p').

#include <stdio.h>
#include <string.h>

int main(void) {
    const char *input = "ExIt";

    if (_stricmp(input, "exit") == 0) {
        printf("Goodbye!\n");
    } else if (_stricmp(input, "help") == 0) {
        printf("Commands: help, exit\n");
    } else {
        printf("Unknown command: %s\n", input);
    }

    return 0;
}

Goodbye!

#include <stdio.h>
#include <string.h>

int main(void) {
    const char *a = "OpenAI";
    const char *b = "openai";

    printf("strcmp:  %d\n", strcmp(a, b));
    printf("_stricmp: %d\n", _stricmp(a, b));

    return 0;
}

strcmp:  -32
_stricmp: 0

#include <stdio.h>
#include <string.h>

#if defined(_WIN32)
  #define ci_compare _stricmp
#else
  #include <strings.h>
  #define ci_compare strcasecmp
#endif

int main(void) {
    const char *a = "Save";
    const char *b = "save";

    if (ci_compare(a, b) == 0) {
        printf("Same command (any case).\n");
    }

    return 0;
}

Same command (any case).

🚀 Common Use Cases

• CLI commands — accept help, HELP, or Help.
• Yes/No prompts — match y, Y, yes, YES.
• Config keys — tolerate case in simple INI-style files (with care).
• Filename checks — on case-insensitive file systems.
• Windows-only tools — natural fit when targeting MSVC without POSIX.

📝 Notes

• Not ISO C—use strcasecmp on POSIX or a wrapper for portability.
• MSVC prefers the name _stricmp in documentation.
• ASCII-centric rules—not full Unicode or locale collation.
• Do not pass NULL pointers—behavior is undefined.
• Not for password comparison or security-sensitive equality.

⚡ Optimization

Runtime libraries optimize case-insensitive compares for typical string lengths. For hot paths, avoid repeated comparisons of the same literals—normalize input once or intern common commands.

💡 Best Practices