Printing name and value of a macro

Question

I have a C program with a lot of optimizations that can be enabled or disabled with #defines. When I run my program, I would like to know what macros have been

Answer 1

Wave library from boost can be helpful also to do what you want. If your project is big enough, I think it is worth trying. It is a C++ preprocessor, but they are the same any way :)

Answer 2

You did not specify the compiler you were using. If this is gcc, gcc -E may help you, as it stops after the preprocessing stage, and prints the preprocessing result. If you diff a gcc -E result with the original file, you may get part of what you want.

Answer 3

Writing a MACRO that expands to another MACRO would require the preprocessor to run twice on it.
That is not done.

You could write a simple file,

// File check-defines.c
int printCompileTimeDefines()
{
#ifdef DEF1
  printf ("defined : DEF1\n");
#else // DEF1
  printf ("undefined: DEF1\n");
#endif // DEF1
// and so on...
}

Use the same Compile Time define lines on this file as with the other files.
Call the function sometime at the start.

If you have the #DEFINE lines inside a source file rather than the Makefile,
Move them to another Header file and include that header across all source files,
including this check-defines.c.

Hopefully, you have the same set of defines allowed across all your source files.
Otherwise, it would be prudent to recheck the strategy of your defines.

---

To automate generation of this function,
you could use the M4 macro language (or even an AWK script actually).
M4 becomes your pre-pre-processor.

Answer 4

Based on Chrisharris, answer I did this. Though my answer is not very nice it is quite what I wanted.

#define STR(x)   #x
#define SHOW_DEFINE(x) printf("%s %s\n", #x, strcmp(STR(x),#x)!=0?"is defined":"is NOT    defined")

Only bug I found is the define must not be #define XXX XXX (with XXX equals to XXX).

Answer 5

It is not possible indeed, the problem being the "not defined" part. If you'd relied on the macro values to activate/deactivate parts of your code, then you could simply do:

#define SHOW_DEFINE(X) \
do { \
if (X > 0) \
    printf("%s %d\n", #X, (int)X);   \
else \
    printf("%s not defined\n", #X);   \
} while(0)