Check if bool is defined in mixed C/C++

Question

So I'm having issues with some code that I've inherited. This code was building fine in a C-only environment, but now I need to use C++ to call this code. The header problem.h contains:

#ifndef _BOOL
typedef unsigned char bool;
static const bool False = 0;
static const bool True = 1;
#endif

struct astruct
{
  bool myvar;
  /* and a bunch more */
}

When I compile it as C++ code, I get error C2632: 'char' followed by 'bool' is illegal

I get the same error if I wrap the #include "problem.h" in extern "C" { ... } (which I don't understand, because there should be no keyword bool when compiling as C?)

I tried removing the block from #ifndef _BOOL to #endif, and compiling as C++, and I get errors:

error C2061: C requires that a struct or union has at least one member
error C2061: syntax error: identifier 'bool'

I just don't understand how the C++ compiler is complaining about a redefinition of bool, yet when I remove the redefinition and try to just use bool to define variables, it doesn't find anything.

Any help is greatly appreciated.

Answer 1

Because bool is a basic type in C++ (but not in C), and can't be redefined.

You can surround your code with

#ifndef __cplusplus
typedef unsigned char bool;
static const bool False = 0;
static const bool True = 1;
#endif

Answer 2

You can use C99's bool:

#ifndef __cplusplus
#include <stdbool.h>
#endif

bool myBoolean; // bool is declared as either C99's _Bool, or C++'s bool data type.

Why should you use this?

For compatibility with other C99 code. _Bool is commonly used in C99 Code, and is very useful. It also grants you the ability to have a boolean datatype without the need to typedef a lot of stuff, as behind the scenes, _Bool is a datatype defined by the compiler.