C++ Preprocessor Macros with relation to Include files

Question

I was just wondering whether the C++ preprocessor is capable of macros such as:

#define include<a> include<a.h>

Which would convert

#include<stdio>

into

#include<stdio.h>

Does anyone have any ideas?

The accepted answer to the duplicate question isn't all that helpful. A number of the other answers are more helpful. The key point is that even if the output of macro processing looks like a preprocessor directive, it is _not_ a preprocessor directive. So you can't generate the `#include` part of the line from a macro. You can, however, generate the file name part of the `#include` line as a macro. You just have to be a bit careful, that's all. — Jonathan Leffler, Dec 27 '14 at 09:01

score 3 · Accepted Answer · answered Dec 27 '14 at 06:11

The #include directives can't be replaced directly with a macro. However, the entity to be included can be the result of a macro expansion. That is, if you need to use different header names, you can define a macro which expands to what is being included, e.g.:

#define CONCAT(a,b) a ## b
#ifdef USE_C_NAMES
#   define MAKE_NAME(x) <x.h>
#else
#    define MAKE_NAME(x) <CONCAT(c,x)>
#endif
#include MAKE_NAME(stdio)

C++ Preprocessor Macros with relation to Include files

1 Answers1