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#include <stdio.h>
#include <string.h>
#include <stdlib.h>
/* The C Programming Language: 2nd Edition
*
* Exercise 7-6: Write a program to compare two files, printing the first line
* where they differ.
*
* Notes: `cat` is a surprisingly small program, and that trend continues with
* this little `diff` rip-off. This could probably be done with sparing,
* careful use of 'goto', but that's generally in the realm of "you better know
* what you're doing". I feel that the code explains itself here.
*/
#define LINE_MAX 200
int max(int x, int y);
int main(int argc, char *argv[]) {
/* Setup the file pointers so we can iterate through them */
FILE *fileA;
FILE *fileB;
char *prog = argv[0];
char line1[LINE_MAX];
char line2[LINE_MAX];
int len1 = 0;
int len2 = 0;
int done = 0;
if (argc != 3) {
fprintf(stderr, "%s: you must compare two files.\n", prog);
exit(1);
}
/* Setup our file pointers */
if ((fileA = fopen(argv[1], "r")) == NULL) {
fprintf(stderr, "%s: could not open file '%s'\n", prog, argv[1]);
exit(2);
}
if ((fileB = fopen(argv[2], "r")) == NULL) {
fprintf(stderr, "%s: could not open file '%s'\n", prog, argv[2]);
exit(2);
}
while (done == 0) {
len1 = fetchline(fileA, line1, LINE_MAX);
len2 = fetchline(fileB, line2, LINE_MAX);
if (len1 == 0 || len2 == 0) {
break;
}
/* If their length is different, then the lines themselves are
* different */
if (len1 != len2) {
done = 1;
break;
}
/* Basic string comparison's all we need to determine if there's a
* match or not. */
if (strcmp(line1, line2) != 0) {
done = 1;
break;
}
}
if (done != 0) {
printf("These lines do not match:\n");
printf("%20s: %s%20s: %s", argv[1], line1, argv[2], line2);
return 0;
}
}
int max(int x, int y) {
return (x > y) ? x : y;
}
/* Stealing this from the book because it makes life simpler */
int fetchline(FILE *fp, char *line, int max) {
if (fgets(line, max, fp) == NULL) {
return 0;
} else {
return strlen(line);
}
}
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