Solve Exercise 5-3: pointer-powered strcat()

1 files changed, 42 insertions, 0 deletions

diff --git a/ch5/5-03_strcatp.c b/ch5/5-03_strcatp.c
new file mode 100644
index 0000000..9bfc336
--- /dev/null
+++ b/ch5/5-03_strcatp.c
@@ -0,0 +1,42 @@
+#include <stdio.h>
+
+/* The C Programming Language, 2nd Edition
+ *
+ * Exercise 5-3: Write a pointer version of the function strcat that we showed
+ * in Chapter 2: strcat(s,t) copies the string t to the end of s.
+ *
+ * Answer: Pay careful attention to the passage before this exercise; there's
+ * a difference between a character array and a pointer to a string constant.
+ * The major difference is you can modify the contents of a character array.
+ * String constants, like other constants, can't be modified. This practically
+ * requires that the first argument to strcatp is a character array.
+ *
+ * When working with pointers, details seem to be of utmost importance.
+ *
+ * Thanks to Chris and dagle from Freenode's ##c for their input on
+ * improving the code.
+ */
+
+#define ALLOC 80
+
+void strcatp(char *s, char *t);
+
+int main(void) {
+	char foo[ALLOC] = "This is amazing!";
+	char *bar = " Pointers for everyone!";
+	strcatp(foo, bar);
+	printf("%s\n", foo);
+	return 0;
+}
+
+/* strcat: copy t into s; s must be large enough */
+void strcatp(char *s, char *t) {
+	while (*s != '\0') {
+		s++;
+	}
+	/* Doing this without checking a buffer means it may screw up memory.
+	 * It's the programmer's duty to ensure this doesn't happen, not the
+	 * function's.
+	 */
+	while ((*s++ = *t++));
+}