Only in someone's legacy code. If you did it yourself (or even if you did not) — get your hands dirty. Sorry, dirt is dirt, it cannot go without hard and unpleasant work.
However, depending on your compiler, increase in warning level to maximum can help to detect some dead code, albeit not completely.
There are different code analysis tools. Try to find some:
http://en.lmgtfy.com/?q=(find+OR+detect+OR+remove)+(unused+OR+dead)+code+automatically+%22C%2B%2B%22[
^]
I don't know you platform, compiler, etc., so see the search results, there are over 10 million, top of the list looks relevant.
—SA