Consider this C/C++ program: extern void **f1(); void f2(const char *p) { *(const void **)f1() = p; }
If I compile this program with g++ -Wcast-qual, I get this: foo2.cc:2: warning: cast from type ‘void**’ to type ‘const void**’ casts away qualifiers If I compile this program with gcc -Wcast-qual, I do not get any warning. Let's overlook the fact that the text of the g++ warning does not make any sense--I am certainly not casting anything away. The warning is conceptually plausible for the same reason that you can't assign a char** variable to a const char** variable without a cast. At least, I think one could make a argument that that is so. But it's not a *very* strong argument, as -Wcast-qual is documented to warn about cases where a type qualifier is removed, and that is manifestly not happening here. -Wcast-qual is useful to catch certain programming errors; I don't think anybody adding a const qualifier is actually making a mistake. All that aside, I can't think of any reason that the C and C++ frontends should be different in this regard. Does anybody want to make an argument for which of these choices we should adopt? 1) Keep things the same: the C++ frontend warns, the C frontend doesn't. Consistency is overrated. 2) Change the C frontend to also warn about this case, albeit with a better message. 3) Change the C++ frontend to not warn about this case. Of course in all cases the frontends should continue to warn about a cast from const void** to void**. Ian