บอกตำแหน่งเริ่มต้นที่ไฟล์ทั้ง 2 ไฟล์ แตกต่างกัน
[code lang=”c”]
//Compare File
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[]) {
FILE *fp1, *fp2;
char ch1, ch2, same;
unsigned long l;

if (argc != 3) {
printf("Usage: compare <file 1> <file 2>\n");
exit(1);
}

/* open first file */
if ((fp1 = fopen(argv[1], "rb")) == NULL) {
printf("Cannot open first file.\n");
exit(1);
}

/* open second file */
if ((fp2 = fopen(argv[2], "rb")) == NULL) {
printf("Cannot open second file.\n");
exit(1);
}

l = 0;
same = 1;
/* compare the files */
while (!feof(fp1)) {
ch1 = fgetc(fp1);
if (ferror(fp1)) {
printf("Error reading first file.\n");
exit(1);
}
ch2 = fgetc(fp2);
if (ferror(fp2)) {
printf("Error reading second file.\n");
exit(1);
}
if (ch1 != ch2) {
printf("Files differ at byte number %lu", l);
same = 0;
break;
}
l++;
}
if (same)
printf("Files are the same.\n");

if (fclose(fp1) == EOF) {
printf("Error closing first file.\n");
exit(1);
}

if (fclose(fp2) == EOF) {
printf("Error closing second file.\n");
exit(1);
}

return 0;
}
[/code]