Producing a list of all the preprocessor symbols defined in headers

Question

Say I use some C or C++ library, made out of headers and some source files, that are compiled into a static or shared library I can link with.

In the headers of the library (dozens... or hundreds of files), some macros/symbols are defined.

Now I want to use this library in a project, that also defines some macros and symbols. Of course, I want to avoid name collisions, as this has been reported sometimes, particularly with windows.h. But more generally I want to keep control of what is really exported out of that header.

I can produce a list of defined symbols with gcc preprocessor options:

gcc -E -dM include/great_lib.h | sort -V >symbols.txt

This outputs in file symbols.txt a sorted list of all the defined symbols included in a user file when it includes this header.

However, it only gives the symbol, not the file where it was defined.

I have the feeling that this could be a useful information. For example, to check if some system macro is being redefined in "great_lib.h" or its ascendants. Unfortunalty, after checking gcc preprocessor options, I don't see a way to do that using gcc.

For example, instead of only giving me:

#define M_PI 3.14159265358979323846

it would produce

#define M_PI 3.14159265358979323846; /usr/include/math.h

Maybe something with the -dN option ? But its output is confusing for me, it requires further text processing, and I don't understand how the information is layered. Or a simpler way ?

Related questions:

• Anyway to see list of preprocessor defined macros?
• How can I get a list of all preprocessor symbols used (or defined) within a file?

Answer 1

The -dD option outputs the preprocessed source along with the macros. This includes lines that indicate the current source file, e.g.

# 1 "c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.2/../../../../include/_mingw.h" 1 3

You can write a little program that (i) keeps track of the current source file by parsing these lines; (ii) outputs all lines that start with #define (and \t# define etc.), followed by the current source filename; (iii) discards all other lines (the source code, declarations etc.).