https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110005
Bug ID: 110005
Summary: Writable strings seem too greedy in overload
resolution
Product: gcc
Version: unknown
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: arthur.j.odwyer at gmail dot com
Target Milestone: ---
I'm not clear on the entire behavior of -Wwrite-strings; bug 61579 seems
relevant. So there's probably an iceberg lurking below the surface. But here's
the tip, anyway.
// https://godbolt.org/z/Y5saPdozT
struct Evil {
Evil(const char*, const void*) { puts("1"); }
Evil(const char*, std::string) { puts("2"); }
Evil(const char*, char*) { puts("3"); }
};
int main() {
Evil e = {"", ""};
}
MSVC considers the only viable candidates #1 and #2.
Clang considers #1 and #2 preferable to #3, but will pick #3 if it's the only
candidate.
GCC considers #3 the *best* candidate, even better than #1.
Or again, something like this:
void f(const char *, std::string) { puts("4"); }
template<class T> void f(T *, std::remove_const_t<T> *) { puts("5");
int main() {
f("", "");
}
MSVC considers #4 the only viable candidate.
Clang considers #4 preferable to #5, but will pick #5 if it's the only
candidate.
GCC considers #5 the *best* candidate, even better than #4.
Obviously MSVC's behavior is the conforming one; but I understand GCC isn't
likely to go all the way *there*. Still, Clang's behavior strikes me as a
better compromise than GCC's.
As a consolation prize, assuming there's some way to turn off GCC's
writable-strings extension, could the text of -Wwrite-strings' warning message
be updated to provide that option? E.g. instead of the current
> warning: ISO C++ forbids converting a string constant to
> 'std::remove_const_t<const char>*' {aka 'char*'} [-Wwrite-strings]
it could say, like,
> warning: ISO C++ forbids converting a string constant to
> 'std::remove_const_t<const char>*' {aka 'char*'}; pass -fno-writable-strings
> to disable this extension [-Wwrite-strings]
or however the extension can actually be disabled.
