Jens Gustedt's Blog

April 2, 2014

Don’t use casts

Filed under: C11, C99, language — Jens Gustedt @ 01:50

I recently reviewed some document on security recommendations where I was baffled by the fact that the code examples were sprinkled with casts all over the place. I had thought that people that are concerned with software security in mind would adhere to one of the most important rules in C programming:

Casts are harmful and evil.

The “evil” here is to be read as reference to black magic. Most uses of cast are merely done in the spirit of “casting a spell” by people that try to quieten their compiler. The sorcerer’s apprentice approach: if I don’t see the evil, it isn’t there.

For me it is evident that every cast punches a hole in C’s type system. So, concerned with code security, we should avoid them as much as possible. But this evidence doesn’t yet seem shared (meaning that it is not so evident 🙂 and I decided to explain things here in more detail.

Casts (explicit conversions) in C come with three different flavors, depending on the cast-to and cast-from type

  1. pointer to pointer
  2. pointer to integer or vice versa
  3. integer to integer


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