macro definition containing #include directive

Question

Is there a way to define a macro that contains a #include directive in its body?

If I just put the \"#include\", it gives the error

Answer 1

C and C++ languages explicitly prohibit forming preprocessor directives as the result of macro expansion. This means that you can't include a preprocessor directive into a macro replacement list. And if you try to trick the preprocessor by "building" a new preprocessor directive through concatenation (and tricks like that), the behavior is undefined.

Answer 2

I think you are all right in that this task seems impossible as I also got from

http://groups.google.com/group/comp.lang.c++/browse_thread/thread/03d20d234539a85c#

No, preprocessor directives in C++ (and C) are not reflective.

Pawel Dziepak

Anyway, the reason behind this attempt is that I am trying to make the following repeatedly used code snippet as a macro:

void foo(AbstractClass object)
{
    switch (object.data_type())
    {
    case AbstractClass::TYPE_UCHAR :
        {
        typedef unsigned char PixelType;
        #include "snippets/foo.cpp"
        }
        break;
    case AbstractClass::TYPE_UINT:
        {
        typedef unsigned int PixelType;
        #include "snippets/foo.cpp"
        }
        break;
    default:
        break;
    }
}

For another task, I need to have a similar function

void bar(AbstractClass object)

where I will place

#include "snippets/bar.cpp"

and of course it is in "snippets/foo.cpp" and "snippets/bar.cpp" that the task-specific code is written.

Answer 3

Contagious is right -- if you're doing:

myFile.c:

#include "standardAppDefs.h"
#myStandardIncludeMacro

standardAppDefs.h:

#define myStandardIncludeMacro #include <foo.h>

Why not just say:

myFile.c:

#include "standardAppDefs.h"

standardAppDefs.h:

#include <foo.h>

And forget the macros?