Check If Bool Is Defined in Mixed C/C++
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...
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.
4 Answers
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
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.
You should use the __cplusplus macro:
#ifndef __cplusplus
#ifndef _BOOL
typedef unsigned char bool;
static const bool False = 0;
static const bool True = 1;
#endif
#endif
Check out this link to the C++ FAQ for further details.
I had this "'char' followed by 'bool' is illegal" problem in VS also. The problem for me was I did not end my class declaration with a semi-colon- which I was not expecting to be the issue as this was in the header file and the problem was coming up in the cpp file! eg:
class myClass
{
}; // <-- put the semi colon !!
Elena Rostova holds a Master's degree in Public Health Journalism. She covers groundbreaking medical research, holistic wellness trends, mental health awareness, and nutritional science.
