cmp.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
//#include <stdint.h>
#include <unistd.h>
#include <fcntl.h>
//#ifdef _WIN32
//#include <winioctl.h>
//#else
//#include <sys/ioctl.h>
//#endif
#include <errno.h>

int main(int argc, char *argv[]) {
	int fd1, fd2;
	char buf1[4096], buf2[4096];
	int res, res1, res2;
	int rv = 0;
	int i;
	int filepos = 0;

	int show_byte = 0;
	int show_all = 0;
	int limit = 0;

	while(1) {
		int c = getopt(argc, argv, "bln:");
		if(c == EOF) break;
		switch(c) {
			case 'b':
				show_byte = 1;
				break;
			case 'l':
				show_all = 1;
				break;
			case 'n':
				limit = atoi(optarg);
				break;
			case '?':
				fprintf(stderr, "%s: invalid option -%c\n", argv[0], optopt);
				exit(1);
		}
	}

	if (optind + 2 != argc) {
		fprintf(stderr, "Usage: %s [-b] [-l] [-n <count>] <file1> <file2>\n", argv[0]);
		exit(1);
	}

	fd1 = open(argv[optind], O_RDONLY);
	if(fd1 == -1) {
		fprintf(stderr, "could not open %s, %s\n", argv[optind], strerror(errno));
		return 1;
	}

	fd2 = open(argv[optind+1], O_RDONLY);
	if(fd2 == -1) {
		fprintf(stderr, "could not open %s, %s\n", argv[optind+1], strerror(errno));
		return 1;
	}

	while(1) {
		res1 = read(fd1, &buf1, sizeof(buf1));
		res2 = read(fd2, &buf2, sizeof(buf2));
		res = res1 < res2 ? res1 : res2;
		if(res1 == 0 && res2 == 0) {
			return rv;
		}
		for(i = 0; i < res; i++) {
			if(buf1[i] != buf2[i]) {
				printf("%s %s differ byte %d", argv[optind], argv[optind+1], filepos + i);
				if(show_byte) printf(" 0x%02x 0x%02x", buf1[i], buf2[i]);
				putchar('\n');
				if(!show_all) return 1;
				rv = 1;
			}
			if(limit) {
				limit--;
				if(limit == 0) return rv;
			}
		}
		if(res1 != res2 || res < 0) {
			printf("%s on %s\n", res < 0 ? "Read error" : "EOF", res1 < res2 ? argv[optind] : argv[optind+1]);
			return 1;
		}
		filepos += res;
	}
}