Functional Programming: A PragPub Anthology

Defect Smashing

We have a reproducible scenario that demonstrates the presence of a memory management bug in our C code. Now that we have a failing test, we need to figure out what is actually wrong with our code. Let’s take another look.

caesar.c
char *caesar(int shift, char *input)
{
  char *output = malloc(strlen(input));
  memset(output, '\0', strlen(input));

  for (int x = 0; x < strlen(input); x++) {
    if (isalpha(input[x])) {
      int c = toupper(input[x]);
      c = (((c - 65) + shift) % 26) + 65;
      output[x] = c;
    } else {
      output[x] = input[x];
    }
  }

  return output;
}

A closer examination reveals the issue. As with most programming problems, there are a few different ways to address this. We will again take the easy way out. ...