I'm trying to write a macro that would allow me to do something like: FORMAT(a << "b" << c << d), and the result would be a string -- the same as creating an ostringstream, inserting a...d, and returning .str(). Something like:
string f(){ ostringstream o; o << a << "b" << c << d; return o.str() }
Essentially, FORMAT(a << "b" << c << d) == f().
First, I tried:
1: #define FORMAT(items) \
((std::ostringstream&)(std::ostringstream() << items)).str()
If the very first item is a C string (const char *), it will print the address of the string in hex, and the next items will print fine. If the very first item is an std::string, it will fail to compile (no matching operator<<).
This:
2: #define FORMAT(items) \
((std::ostringstream&)(std::ostringstream() << 0 << '\b' << items)).str()
gives what seems like the right output, but the 0 and \b are present in the string of course.
The following seems to work, but compiles with warnings (taking address of temporary):
3: #define FORMAT(items) \
((std::ostringstream&)(*((std::ostream*)(&std::ostringstream())) << items)).str()
Does anyone know why 1 prints the address of the c-string and fails to compile with the std::string? Aren't 1 and 3 essentially the same?
I suspect that C++0x variadic templates will make format(a, "b", c, d) possible. But is there a way to solve this now?