[boost] [format] Variable argument list and string assembly

From: Stephan Menzel (smenzel_at_[hidden])
Date: 2007-07-31 16:34:48

Hi all,

I'd like to create a method using some sort of variable argument list like it 
would be in printf style:

foo(int code, const char *fmt, ...) {}
...but using boost format.
Basically, the function shall compute the format string and than create a new 
string with the number in "code" in front of it and the result of the 
computed format following. It's for returning standard replies and do some 
stuff depending on the error code. And it must be as performant as 
reasonable.

I only came up with something like this:

void foo(int code, boost::format &fmt) {

        boost::format retfrmt("%d - message: ");
        retfrmt % code;
        std::cout << retfrmt.str().append(fmt.str()) << std::endl;
}

int main(int argc, char **argv) {

        reply(42, boost::format("%d test %s\n") % 23 % "Hello");
        return 0;
}

which does what I expected:

42 - message: 23 test Hello

But I don't like the usage a lot. Especially the fact that I have to write 
boost::format(...) when using the function. (could use a macro so that's not 
the killer issue) Also there seems to be a lot of unnecessary string copying 
involved so I wonder if this is a good way to do this. Is there any better 
solution to this?

Thanks and greetings...

Stephan