---
name: "strncmp"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/strncmp"
---

# strncmp(3)

nonstrings compare

## NAME

strncmp - nonstrings compare

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

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

**int strncmp(const char** s1**\[\], const char** s2**\[\], size\_t** n**);**

## DESCRIPTION

The **strncmp**() function is similar to [**strcmp**(3)](/strcmp/3.md), except it compares only the first (at most) *n* bytes of *s1* and *s2*.

It is equivalent to

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

## RETURN VALUE

See [**memcmp**(3)](/memcmp/3.md).

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **strncmp**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

POSIX.1-2001, C89, SVr4, 4.3BSD.

## EXAMPLES

The program below can be used to demonstrate the operation of **strncmp**().

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

### 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);
}
```

## SEE ALSO

[**memory.h**(3head)](/memory.h/3head.md), [**memcmp**(3)](/memcmp/3.md), [**strncasecmp**(3)](/strncasecmp/3.md), [**wcsncmp**(3)](/wcsncmp/3.md)