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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 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 exam‐
       ples 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  un‐
       signed 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)

                                                                               2021-03-22                                                                      STRCMP(3)