How to change macro function argument expansion ordering? - c++

Question

I have the following code:
#include <iostream>
#include <stdexcept>
#define TRACE_MACRO(EnterText) \
class CTrace \
{ \
public: \
CTrace() \
{ \
std::cout << EnterText; \
} \
private:\
};
#define DO_TRACE TRACE_MACRO("[ENTER] " __FUNCTION__ "\r\n") CTrace trace
static void test()
{
DO_TRACE;
}
int main(int, char**)
{
DO_TRACE;
test();
return 0;
}
Which outputs:
[ENTER] main::CTrace::CTrace
[ENTER] test::CTrace::CTrace
How can I write the macro such that __FUNCTION__ is expanded first so that the output becomes:
[ENTER] main
[ENTER] test
I attempted to create a sub macro called DO_TRACE2 that forwards the arguments, but this results in the same output.
If this isn't possible then what about a macro that will compile time substring the text to strip off the CTrace::CTrace part of the string?
Edit: Note that I don't want to pass a pointer to a compile time string to this class, I want the call to std::cout to appear as if I had actually manually wrote std::cout << "main";

Answer 1

Untested, but here's a simple rearrangement that might work:
#define TRACE_MACRO \
class CTrace \
{ \
public: \
CTrace(const char* text) \
{ \
std::cout << text; \
} \
private:\
};
#define DO_TRACE TRACE_MACRO CTrace trace("[ENTER] " __FUNCTION__ "\r\n")

Answer 2

Jimmy asked
is it necessary to define a whole new class in the macro def?
And you replied:
#Jimmy no, I just wanted the call to std::cout to be using const
static compile time strings rather than a pointer to a compile time
string, if that makes sense.
So why not just drop the class:
#define DO_TRACE std::cout << "[ENTER] " << __FUNCTION__ << "\r\n"
This will output:
[ENTER] main
[ENTER] test
and uses the const static compile time string....
I probably missed something, just tell me, I'll delete this post....
By the way, I compiled the code from your post using GNU GCC version 4.8.1 from http://www.compileonline.com/compile_cpp_online.php. It outputs
[ENTER] CTrace
[ENTER] CTrace
So looks like FUNCTION macro is resolved differenetly by compilers...