Any utility to test expand C/C++ #define macros?

Question

Go to https://godbolt.org/. Enter your code in the left pane and select compiler as gcc put the argument as -E in the right pane. Your pre-processed code will appear on the right.

You can just run your code through the preprocessor, which will show you what it will be expanded into (or spit out errors as necessary):

$ cat a.c
#define GETADDR_FOR(a) if (!(a = (#_#a)GetProcAddress(h, "/""#a"/""))) 
GETADDR_FOR(hexdump)

$ gcc -E a.c
# 1 "a.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "a.c"
a.c:1:36: error: '#' is not followed by a macro parameter

GETADDR_FOR(hexdump)

In GCC, it's gcc -E foo.c to only preprocess the file.

Visual Studio uses the /P argument.

http://visualstudiogallery.msdn.microsoft.com/59a2438f-ba4a-4945-a407-a1a295598088 - visual studio plugin to expand macroses

You appear to be confused about what the exact syntax is for stringifying or token pasting in C preprocessor macros.

You might find this page about C preprocessor macros in general helpful.

In particular, I think this macro should read like this:

#define GETADDR_FOR(a) if (!(a = (_##a)GetProcAddress(h, #a))) --iFail

The trailing ; should be skipped because you will likely be typing this as GETADDR_FOR(hexdump);, and if you don't it will look very strange in your C code and confuse many syntax highlighters.

And as someone else mentioned gcc -E will run the preprocessor and skip the other compilation steps. This is useful for debugging preprocessor problems.

You might want to take a look at Boost Wave. Like most of Boost, it's really more a library than a utility, but it does have a driver to act as a complete preprocessor.