strcmp, strncmp - compare two strings

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ strcmp(), strncmp()                                                         │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

       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.

       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_compABCABC
           <str1> and <str2> are equal
           $ ./string_compABCAB      # 'C' is ASCII 67; 'C' - '\0' = 67
           <str1> is greater than <str2> (67)
           $ ./string_compABAABZ     # 'A' is ASCII 65; 'Z' is ASCII 90
           <str1> is less than <str2> (-25)
           $ ./string_compABJABC
           <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_compABCAB3
           <str1> is greater than <str2> (67)
           $ ./string_compABCAB2
           <str1> and <str2> are equal in the first 2 bytes

   Programsource

       /* 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);
       }

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

       Standard C library (libc, -lc)

       strcmp, strncmp - compare two strings

       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.

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

Linux man-pages 6.9.1                              2024-06-15                                          strcmp(3)

       C11, POSIX.1-2008.

#include<string.h>intstrcmp(constchar*s1,constchar*s2);intstrncmp(constchars1[.n],constchars2[.n],size_tn);

       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 unsignedchar)  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.)