NAME

       strcmp, strncmp - compare two strings

SYNOPSIS

       #include <string.h>

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

DESCRIPTION

       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

       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

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

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

CONFORMING TO

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

NOTES

       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

       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

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

COLOPHON

       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)