问题
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 the bigger question is whether there is any utility someone could recommend, to quickly display what a macro is actually doing? It seems like even the slow trial and error process would go much faster if I could see what is wrong.
Currently, I'm dynamically loading a long list of functions from a DLL I made. The way I've set things up, the function pointers have the same nanes as the exported functions, and the typedef(s) used to prototype them have the same names, but with a prepended underscore. So I want to use a define to simplify assignments of a long long list of function pointers.
For example, In the code statement below, 'hexdump' is the name of a typedef'd function point, and is also the name of the function, while _hexdump is the name of the typedef. If GetProcAddress() fails, a failure counter in incremented.
if (!(hexdump = (_hexdump)GetProcAddress(h, "hexdump"))) --iFail;
So let's say I'd like to replace each line like the above with a macro, like this...
GETADDR_FOR(hexdump )
Well this is the best I've come up with so far. It doesn't work (my // comment is just to prevent text formatting in the message)...
// #define GETADDR_FOR(a) if (!(a = (#_#a)GetProcAddress(h, "/""#a"/""))) --iFail;
And again, while I'd APPRECIATE an insight into what silly mistake I've made, it would make my day to have a utility that would show me the error of my ways, by simply plugging in my macro.
回答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.
回答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.
回答3:
http://visualstudiogallery.msdn.microsoft.com/59a2438f-ba4a-4945-a407-a1a295598088 - visual studio plugin to expand macroses
回答4:
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.
回答5:
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.
来源：https://stackoverflow.com/questions/3019609/any-utility-to-test-expand-c-c-define-macros