Error declaring default argument to friend function

This is a discussion on Error declaring default argument to friend function within the C++ Programming forums, part of the General Programming Boards category; I'm stumped. This only gives me an error if the class is a template and the functions are declared within ...

  1. #1
    Guest Sebastiani's Avatar
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    Question Error declaring default argument to friend function

    I'm stumped. This only gives me an error if the class is a template and the functions are declared within the class. Here's a stripped-down example:

    Code:
    template < typename T >
    struct foo
    {
        friend void bar( foo< T > const& data, bool condition = false )
        {    }
        
        friend void qux( foo< T > const& data )
        {        
            bar( data );
        }
    };
    
    int main( void )
    {
        qux( foo< int >( ) );
        return 0;
    }
    The error doesn't make much sense either:

    "default argument given for parameter 2 of `void bar(const foo<int>&, bool)' after previous specification in `void bar(const foo<int>&, bool)'.

    Any ideas?
    Code:
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
    {
        return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;
    }

  2. #2
    Guest Sebastiani's Avatar
    Join Date
    Aug 2001
    Location
    Waterloo, Texas
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    5,708
    OK, well, I think I've got it now. Seems as though friend functions (of templates) are supposed to be declared as templates themselves (even if within the class). I didn't think it was necessary since it usually compiles without complaint; I just figured that the compiler was deducing the parameter (given that it's declared within the class, after all). That would be the most logical thing to do, anyway. Go figure.
    Last edited by Sebastiani; 07-05-2009 at 01:55 AM.
    Code:
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
    {
        return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;
    }

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