Make error

[tanim87]

Dear Concern,
While making the fmt, I am getting the following error:
Building CXX object test/CMakeFiles/format-test.dir/format-test.cc.o
/usr/local/src/fmt/test/format-test.cc:1487:20: error: call to 'ptr' is ambiguous

Would you please help me with it?
I am using Ubuntu 16.04

Thanks.

[alexezeder]

Could you please provide compiler info?

[tanim87]

gcc 8.1.0

[alexezeder]

Looks like it should just work with the master branch of {fmt} on Compiler Explorer.
Do you have full output for this error, like function candidates, since the call is ambiguous?

[tanim87]

I have attached the complete screenshot. I could not find log file that would give more insight. Let me know if this will work. Thanks.

[alexezeder]

Thanks, this definitely helped. For some reason, this specific version of GCC is able to decay function pointers to void pointers, just like MSVC, so this branch should be disabled for this GCC version too:

fmt/include/fmt/format.h

Lines 3837 to 3844 in 7e72673

	#if !FMT_MSC_VER
	// MSVC lets function pointers decay to void pointers, so this
	// overload is unnecessary.
	template <typename T, typename... Args>
	inline const void* ptr(T (*fn)(Args...)) {
	return detail::bit_cast<const void*>(fn);
	}
	#endif

You can check it locally just by commenting out the code above.

But since I don't know how to make it in a more versatile way, I think we should just wait for more experienced people for proper fix.

[vitaut]

I think we could SFINAE this overload away on function to const void* pointer convertibility.

[alexezeder]

Actually there is another problem with fmt::ptr and old Clang versions (<7.0) - https://godbolt.org/z/j57Kzx. Actually, this problem is even more interesting than I thought - https://godbolt.org/z/sEsTE7.

But as far as I can see, following workarounds are able to satisfy all compilers - https://godbolt.org/z/Y8sadG. I'll create a PR with this code soon.

[tanim87]

Your suggestion worked! Thanks.