[Warning] When passing const reference and default value

[Mathieu Malaterre <mmalater at nycap dot rr dot com>]

Hello,

	I was just wondering should the following code (*) produce a warning 
when being compiled or not? I would tend to say yes, it should. If not 
could someone explain me how the compiler could produce a string 
reference out of the default const char * value ?

Thanks
Mathieu

(*)
#include <string>
#include <iostream>

void foo(std::string const & s = "bar" )
{
 std::cout << s << std::endl;
}


int main()
{
 foo( );
 return 0;
}

//////////////////
// compilation line:

g++ -W -Wall -pedantic warn.cxx