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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.
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
The include path problem is solved by using gcc -E and passing the include directory with the -I option
367
The LENGTH and BREADTH are called the macro templates. The values 10 and 20 are called macro expansions. When the program run and if the C preprocessor sees an instance of a macro within the program code, it will do the macro expansion. It replaces the macro template with the value of macro expansion.
Macro expansion is an integral part of eval and compile . Users can also expand macros at the REPL prompt via the expand REPL command; See Compile Commands. Macros can also be expanded programmatically, via macroexpand , but the details get a bit hairy for two reasons. The second complication involves eval-when .
Macro expansion is always just a textual transform of the input source code. You should be able to see the code after the pre-processor (the part of the compilation that does the macro expansion) is done; this text is what the compiler proper then works on.
The C preprocessor is a macro preprocessor (allows you to define macros) that transforms your program before it is compiled. These transformations can be the inclusion of header files, macro expansions, etc. All preprocessing directives begin with a # symbol. For example, #define PI 3.14.
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; } If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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