ex27

lcthw-remnants-2/ex27.c

@@ -0,0 +1,74 @@
+#undef NDEBUG
+#include "dbg.h"
+#include <stdio.h>
+#include <assert.h>
+
+/*
+ * naive copy that assumes all inputs are always valid
+ * taken from K&R C and cleaned up a bit;
+ */
+void copy(char to[], char from[])
+{
+  int i = 0;
+
+  // while loop will not end if from isn't '\0' terminated
+  while((to[i] = from[i]) != '\0') {
+    ++i;
+  }
+}
+
+/*
+ * A safer version that checks for many common errors using the
+ * length of each string to control the loops and termination.
+ */
+int safercopy(int from_len, char *from, int to_len, char *to)
+{
+  assert(from != NULL && to != NULL && "from and to can't be NULL");
+  int i = 0;
+  int max = from_len > to_len - 1 ? to_len - 1 : from_len;
+
+  // to_len must have at least 1 byte
+  if(from_len < 0 || to_len <= 0) return -1;
+
+  for(i = 0; i < max; i++) {
+    to[i] = from[i];
+  }
+
+  to[to_len - 1] = '\0';
+
+  return i;
+}
+
+
+int main(int argc, char *argv[])
+{
+  // careful to understand why we can get these sizes
+  char from[] = "0123456789";
+  int from_len = sizeof(from);
+
+  // notice that it's 7 chars + \0
+  char to[] = "0123456";
+  int to_len = sizeof(to);
+
+  debug("Copying '%s':%d to '%s':%d", from, from_len, to, to_len);
+
+  int rc = safercopy(from_len, from, to_len, to);
+  check(rc > 0, "Failed to safercopy.");
+  check(to[to_len - 1] == '\0', "String not terminated.");
+
+  debug("Result is '%s':%d", to, to_len);
+
+  // now try to break it
+  rc = safercopy(from_len * -1, from, to_len, to);
+  check(rc == -1, "safercopy should fail #1");
+  check(to[to_len - 1] == '\0', "String not terminated.");
+
+  rc = safercopy(from_len, from, 0, to);
+  check(rc == -1, "safercopy should fail #2");
+  check(to[to_len - 1] == '\0', "String not terminated.");
+
+  return 0;
+
+error:
+  return 1;
+}