How to concat __func__ and __LINE__ in a macro definition

I would like to define a macro to concat __func__ (or __FUNCTION__) with __LINE__:

The following works fine:

// macro_test.cc#include <iostream>#define STR2(X) #X#define STR(X) STR2(X)#define FILE_LOCATION __FILE__ ":" STR(__LINE__) ""int main() {  std::cout << FILE_LOCATION << "is <file_name>:<line_number>"<< std::endl;  return 0;}

And here is the output

$ ./a.out macro_test.cc:8 is <file_name>:<line_number>

However the following gives a compilation error (I just replaced__FILE__ with __func__):

// macro_test.cc#include <iostream>#define STR2(X) #X#define STR(X) STR2(X)#define FUNC_LOCATION __func__ ":" STR(__LINE__) ""int main() {  std::cout << FUNC_LOCATION << "is <function_name>:<line_number>"<< std::endl;  return 0;}~$ gcc macro_test.cc macro_test.cc: In function ‘int main()’:macro_test.cc:5:32: error: expected ‘;’ before string constant #define FUNC_LOCATION __func__ ":" STR(__LINE__) ""                                ^macro_test.cc:8:16: note: in expansion of macro ‘FUNC_LOCATION’   std::cout << FUNC_LOCATION << "is <function_name>:<line_number>"<< std::endl;

Does anyone know the reason for this and how can I achieve this?

I am using gcc 5.4.0 on Linux (Ubuntu 18.04).