STRCMP(3)



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

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  str-
       coll(3)).  The comparison is done using unsigned characters.

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

       o 0, if the s1 and s2 are equal;

       o a negative value if s1 is less than s2;

       o 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 at-
       tributes(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 non-zero 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 dif-
       ference 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' - ' ' = 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  con-
       taining  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 characters\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),   strn-
       casecmp(3), strverscmp(3), wcscmp(3), wcsncmp(3), ascii(7)

COLOPHON
       This  page  is  part of release 5.07 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/.

                                  2020-04-11                         STRCMP(3)

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