From 54b3475b3041bf35c25bfad2f521d5751e6eadbf Mon Sep 17 00:00:00 2001
From: zlg <zlg@zlg.space>
Date: Thu, 17 Nov 2016 07:34:18 -0800
Subject: Solve Exercise 7-6: simple `diff` utility

---
 ch7/7-06_simple-diff.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 ch7/7-06_simple-diff.c

diff --git a/ch7/7-06_simple-diff.c b/ch7/7-06_simple-diff.c
new file mode 100644
index 0000000..ba0c58f
--- /dev/null
+++ b/ch7/7-06_simple-diff.c
@@ -0,0 +1,81 @@
+#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 mygetline(char *line, int max);
+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);
+	}
+}
-- 
cgit v1.2.3-54-g00ecf