strncmp(3)

💖 strncmp(3) 💖

okay bestie, so this is strncmp from the Library Functions Manual, and honestly? she's a baddie. let's get into it 🦋

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✨ NAME ✨

strncmp — nonstrings compare

no bc why does the manpage call it "nonstrings" 😭 iconic of her actually

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📚 LIBRARY 📚

Standard C library (libc, -lc) 💅

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🌸 SYNOPSIS 🌸

#include <string.h>  // see memory.h(3head)

int strncmp(const char s1[], const char s2[], size_t n);

like yes, include the header, yes, here's the signature, and yes, it eats a size_t n. periodt. 👑

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💫 DESCRIPTION 💫

So strncmp() is basically strcmp(3)'s cousin who knows when to stop talking. She compares only the first (at most) n bytes of s1 and s2. like, n bytes MAX, she's not doing overtime for free.

It is equivalent to:

memcmp(s1, s2, MIN(MIN(strnlen(s1,n),strnlen(s2,n))+1, n))

no cap, that's literally the formula. copy it, don't @ me. 🔥

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🎀 RETURN VALUE 🎀

See memcmp(3). that's it, that's the section. she's pointing you to her sister's page, iykyk 💅

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👑 ATTRIBUTES 👑

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

• Interface: strncmp()
• Attribute: Thread safety
• Value: MT-Safe

(mt-safe means she can hang out in multiple threads at once and there's no drama 💜)

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🌈 STANDARDS 🌈

C11, POSIX.1-2008. certified, validated, official. 🫶

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📜 HISTORY 📜

POSIX.1-2001, C89, SVr4, 4.3BSD. she's been around, she's got lore, she's an elder icon. ✨

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🧚 EXAMPLES 🧚

okay so this little program below can be used to demonstrate the operation of strncmp(). watch her work:

$ ./strncmp ABC AB 3;
<strn1> is greater than <strn2> (67)
$ ./strncmp ABC AB 2;
<strn1> and <str2> are equal in the first 2 bytes

see how the second one is equal in the first 2 bytes? that's the n doing its thing bestie, she stopped comparing early and called it a tie 💖

🍓 Program source 🍓

// strncmp.c
// Licensed under GNU General Public License v2 or later.

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

int
main(int argc, char *argv[])
{
    int res;

    if (argc != 4) {
        fprintf(stderr, "Usage: %s <strn1> <strn2> <n>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    res = strncmp(argv[1], argv[2], atoi(argv[3]));

    if (res == 0) {
        printf("<strn1> and <strn2> are equal");
        printf(" in the first %d bytes\n", atoi(argv[3]));
        printf("\n");
    } else if (res < 0) {
        printf("<strn1> is less than <strn2> (%d)\n", res);
    } else {
        printf("<strn1> is greater than <strn2> (%d)\n", res);
    }

    exit(EXIT_SUCCESS);
}

ate the whole thing, no crumbs. 💅

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🔗 SEE ALSO 🔗

• memory.h(3head)
• memcmp(3)
• strncasecmp(3)
• wcsncmp(3)

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and that's the tea bestie 🫖 go read your other manpages, they miss you. this was Linux man-pages 6.20, dated 2026-08-10, signing off with a little wave 👋💜 mwah!