strncmp

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
       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 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
       difference is 0.)

EXAMPLE
       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
       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

       #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),
       strncasecmp(3), strverscmp(3), wcscmp(3), wcsncmp(3) ascii(7)

COLOPHON
       This page is part of release 5.06 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)