Question

I have code for bool typedef

typedef enum bool {
    false,
    true,
} bool;

in two headers files if it is not included in the ultimate parent header file, child C files cannot, of course, use type bool, though children of the lesser header file that also defines it can.

However if I define it in the ultimate parent header file then the lesser header file definition errors with “bool has already been declared in the current scope”

I need a solution for the lesser header where it may be included on a project that may or may not have already defined bool… What is the best way to do this??

Ta

Answer 1

First of all, if you’re working with a C99 compiler or later, there’s already a standard Boolean type defined in stdbool.h.

Secondly, you can usually avoid testing against true and false values directly, and I’ve found over the years that this actually leads to code that’s a little easier to read and less error-prone (that’s just a personal opinion, though — YMMV).

The immediate solution is to surround your typedefs with an include guard:

#ifndef BOOL_DEFINED
#define BOOL_DEFINED
typedef enum bool {
  false,
  true
} bool;
#endif

This will keep the type from being declared more than once. However, as you’ve discovered, putting the same type definition in two different headers is a recipe for heartburn. It would be better to put the definition in its own header file (with the include guards as shown above), and then include that file where necessary.