Identifying Unused Functions in C/C++ [duplicate]

问题:

Possible Duplicate:
Finding “dead code” in a large C++ legacy application

My project has a lots of C source files each with a lots of global functions. Many of these are no longer referenced by any caller at all. Is there a simple way to identify which of these functions are not referenced by anyone at all?

The map file generated by VC seems to be useful. But I am not sure exactly how/when a function name is listed in the map file.

回答1:

You can use CCCC (free, open source) which gives you lots of metrics about your program. Another option would be Coverity (not free).

This question may be a duplicate of this one: Dead code detection in legacy C/C++ project

回答2:

I don't think that the map file will be of any use. If it's like other map files I've seen, it won't indicate where (if anywhere) a symbol is used—only where it is defined. What you can do is run dumpbin over your object files: dumpbin /relocations, for example, will in fact display every use of a symbol with an address which may need relocation (practically speaking, functions and variables with static lifetime). You then use your usual tools on the output to determine whether the function you are interested in is there or not. (As someone who has worked mostly on Unix, I've installed CygWin and would use grep. I'm not familiar with the native equivalents to the different Unix tools under Windows.)

It would be fairly simple (using Python, or some similar scripting language) to write a small script which would parse the output of dumpbin /symbols for each of your object files, to get the names of all of the functions you've defined, then parses the output of dumpbin /relocations to give you a list of the functions you use, and finally does the diff of the two. (Microsoft seems to have gone out of their way to make the output of dumpbin difficult to use, but it's still not that difficult; you just have to know which lines to ignore.)

回答3:

A straightfoward but laborious way of doing this is simply to wrap the function declaration and definitions of any suspect functions with preprocessor directives:

#if 0
void old_func();
#endif

...

#if 0
void old_func()
{
}
#endif

or if you want to have more control, you can replace 0 with and actual macro of your own so #if 0 becomes #ifdef NO_OLD_FUNCTIONS - that way it's easier to find and take them out permenantly at a later stage once you're happy they're not used.

Naturally, you'll need to fully compile and link the code and any other code that builds on it.