Seeing expanded C macros

Question

If I want to expand a C macro, what are some good ways to do that (besides tracing it manually)?

For instance, GTK_WIDGET_SET_FLAGS, it uses a macro that uses a macro that uses a macro (or two) ...

I want to just see it somehow expanded automagically, instead of searching for every macro, every step of the way.

UPDATE

I tried cpp, but it seemed to only do the first pass

on:

GTK_WIDGET_SET_FLAGS(obj, 13) 

I got the include file expanded, and then:

G_STMT_START{ ((GTK_OBJECT_FLAGS (obj)) |= (13)); }G_STMT_END 

This is explained by these error message I get this on stderr (when using -o filename)

 gtk/gtkwidget.h:34:21: gdk/gdk.h: No such file or directory gtk/gtkwidget.h:35:31: gtk/gtkaccelgroup.h: No such file or directory gtk/gtkwidget.h:36:27: gtk/gtkobject.h: No such file or directory gtk/gtkwidget.h:37:31: gtk/gtkadjustment.h: No such file or directory gtk/gtkwidget.h:38:26: gtk/gtkstyle.h: No such file or directory gtk/gtkwidget.h:39:29: gtk/gtksettings.h: No such file or directory gtk/gtkwidget.h:40:21: atk/atk.h: No such file or directory 

the gtk, atk, and gdk directories are all in the current working directory, so how do I let cpp search in it?

btw, gcc -E gives the exact same output as cpp

Update2:

The include path problem is solved by using gcc -E and passing the include directory with the -I option

Answer 1

Depending on which compiler you use, there should be a way to see the code after the preprocessor (which does the macro expansion, macros are not known by the compiler at all) is done.

With gcc, the option is -E. Here's a simplified example, using toy code and not the actual GTK+ macro:

~/tmp> cat cpptest.c #define SET_FLAGS(w, f) ((w)->flags |= (f))  int main(void) {         SET_FLAGS(0, 4711);          return 0; } ~/tmp> gcc -E cpptest.c # 1 "cpptest.c" # 1 "<built-in>" # 1 "<command line>" # 1 "cpptest.c"   int main(void) {  ((0)->flags |= (4711));   return 0; }