#include <string.h> int strcmp(const char *s1, const char *s2); int strncmp(const char *s1, const char *s2, size_t n);
strcmp() returns an integer indicating the result of the comparison, as follows:
The strncmp() function is similar, except it compares only the first (at most) n bytes of s1 and s2.
| Interface | Attribute | Value |
| strcmp(), strncmp() | Thread safety | MT-Safe |
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.)
$ ./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
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);
}