宏作为函数参数的默认参数

Question

I'm writing logger file. I'd prefer to use macros __FUNCTION__ there. I don't like the way like:

Logger.write("Message", __FUNCTION__);

Maybe, it's possible to make something like:

void write(const string &message, string functionName = __FUNCTION__)
{
   // ...
}

If not, are there any ways to do that stuff not by hands (I mean passing function name)?

Answer 1

You could do something like that by wrapping it all in a macro:

#define log(msg) Logger.write(msg, __FUNCTION__)

The downside is that you will need to have Logger in scope when using this macro.

Answer 2

Macros work just by text substitution - the preprocessor puts the macro definition in place of its name. You can't have "intelligent" macros like the one you suggest.

There is no support for what you want in standard C++.

Answer 3

You can finally do it without macros magic in c++20:

void write(std::string_view message, const std::source_location& location =
                                         std::source_location::current()) {
  std::cout << "Message= " << message
            << ", Function=" << location.function_name();
}

int main() { 
  write("Hello world!"); 
}