strcmp(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON

STRCMP(3)               Linux Programmer's Manual              STRCMP(3)

NAME         top

       strcmp, strncmp - compare two strings

SYNOPSIS         top

       #include <string.h>

       int strcmp(const char *s1, const char *s2);
       int strncmp(const char *s1, const char *s2, size_t n);

DESCRIPTION         top

       The strcmp() function compares the two strings s1 and s2.  The
       locale is not taken into account (for a locale-aware comparison,
       see strcoll(3)).  The comparison is done using unsigned
       characters.

       strcmp() returns an integer indicating the result of the
       comparison, as follows:

       • 0, if the s1 and s2 are equal;

       • a negative value if s1 is less than s2;

       • a positive value if s1 is greater than s2.

       The strncmp() function is similar, except it compares only the
       first (at most) n bytes of s1 and s2.

RETURN VALUE         top

       The strcmp() and strncmp() functions return an integer less than,
       equal to, or greater than zero if s1 (or the first n bytes
       thereof) is found, respectively, to be less than, to match, or be
       greater than s2.

ATTRIBUTES         top

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

       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │Interface                             Attribute     Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │strcmp(), strncmp()                   │ Thread safety │ MT-Safe │
       └──────────────────────────────────────┴───────────────┴─────────┘

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

NOTES         top

       POSIX.1 specifies only that:

              The sign of a nonzero return value shall be determined by
              the sign of the difference between the values of the first
              pair of bytes (both interpreted as type unsigned char)
              that differ in the strings being compared.

       In glibc, as in most other implementations, the return value is
       the arithmetic result of subtracting the last compared byte in s2
       from the last compared byte in s1.  (If the two characters are
       equal, this difference is 0.)

EXAMPLES         top

       The program below can be used to demonstrate the operation of
       strcmp() (when given two arguments) and strncmp() (when given
       three arguments).  First, some examples using strcmp():

           $ ./string_comp ABC ABC
           <str1> and <str2> are equal
           $ ./string_comp ABC AB      # 'C' is ASCII 67; 'C' - '\0' = 67
           <str1> is greater than <str2> (67)
           $ ./string_comp ABA ABZ     # 'A' is ASCII 65; 'Z' is ASCII 90
           <str1> is less than <str2> (-25)
           $ ./string_comp ABJ ABC
           <str1> is greater than <str2> (7)
           $ ./string_comp $'\201' A   # 0201 - 0101 = 0100 (or 64 decimal)
           <str1> is greater than <str2> (64)

       The last example uses bash(1)-specific syntax to produce a string
       containing an 8-bit ASCII code; the result demonstrates that the
       string comparison uses unsigned characters.

       And then some examples using strncmp():

           $ ./string_comp ABC AB 3
           <str1> is greater than <str2> (67)
           $ ./string_comp ABC AB 2
           <str1> and <str2> are equal in the first 2 bytes

   Program source

       /* string_comp.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 < 3) {
               fprintf(stderr, "Usage: %s <str1> <str2> [<len>]\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           if (argc == 3)
               res = strcmp(argv[1], argv[2]);
           else
               res = strncmp(argv[1], argv[2], atoi(argv[3]));

           if (res == 0) {
               printf("<str1> and <str2> are equal");
               if (argc > 3)
                   printf(" in the first %d bytes\n", atoi(argv[3]));
               printf("\n");
           } else if (res < 0) {
               printf("<str1> is less than <str2> (%d)\n", res);
           } else {
               printf("<str1> is greater than <str2> (%d)\n", res);
           }

           exit(EXIT_SUCCESS);
       }

SEE ALSO         top

       bcmp(3), memcmp(3), strcasecmp(3), strcoll(3), string(3),
       strncasecmp(3), strverscmp(3), wcscmp(3), wcsncmp(3), ascii(7)

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

                               2021-03-22                      STRCMP(3)

Pages that refer to this page: bash(1)bcmp(3)hsearch(3)memcmp(3)qsort(3)scandir(3)selinux_file_context_cmp(3)strcasecmp(3)strcoll(3)string(3)strverscmp(3)strxfrm(3)wcscmp(3)wcsncmp(3)signal-safety(7)