jammy (3) strncmp.3.gz

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' - ' ' = 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 5.10 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)