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

Question

It seems I often spend way too much time trying to get a #define macro to do exactly what i want. I\'ll post my current dilemma below and any help is appreciated. But really

Answer 1

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.

Answer 2

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.

Answer 3

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

Answer 4

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.

Answer 5

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.