function whith default parameters

mmm...
so i decide to use different function..
one whith x and y and one y and z whith the same name..
the class permit it , so itn't wrong!..
anyone have another idea?..
@laserlight : good idea!!..but is a litle bit hard..

thanks to all!!..

Quote:

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Originally Posted by laserlight

I think that neither function overloading nor variadic functions will cut it here. What is needed is named arguments, which is not a feature of C++. The reason is that there is nothing to differentiate foo(x, y) from a call to foo(x, z) or foo(y, z).

I am not sure if this really is a good idea, but I would propose a workaround with std::map and some function templates:

Code:

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#include <iostream>
#include <map>

template<char c1>
std::map<char, int> make_values(int v1)
{
    std::map<char, int> ret;
    ret[c1] = v1;
    return ret;
}

template<char c1, char c2>
std::map<char, int> make_values(int v1, int v2)
{
    std::map<char, int> ret;
    ret[c1] = v1;
    ret[c2] = v2;
    return ret;
}

template<char c1, char c2, char c3>
std::map<char, int> make_values(int v1, int v2, int v3)
{
    std::map<char, int> ret;
    ret[c1] = v1;
    ret[c2] = v2;
    ret[c3] = v3;
    return ret;
}

void foo(const std::map<char, int>& values)
{
    std::map<char, int>::const_iterator iter = values.find('x');
    int x = (iter == values.end()) ? 0 : iter->second;
    iter = values.find('y');
    int y = (iter == values.end()) ? 0 : iter->second;
    iter = values.find('z');
    int z = (iter == values.end()) ? 0 : iter->second;

    std::cout << x << ' ' << y << ' ' << z << std::endl;
}

int main()
{
    foo(make_values<'x'>(1));
    foo(make_values<'z', 'y'>(10, 20));
    foo(make_values<'y', 'x', 'z'>(2, 3, 4));
}

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Hmm... std::vector<std::pair<char, T> > would have been easier too look at. But I think it's not worth the effort. This makes the calling code and the implementation (and not just the interface/prototype) too strongly coupled. Not worth it, no. The OP must accept the fact that what he wants does not make sense in C++ (and many other lnaguages as well). He just have to have default arguments in the order as it is supposed to be or pass the default argument values while making the call or have overloads if they can be implemented (needs default arguments to be of different types else overloading doesnt work either).

Otherwise, have some kind of a message format (XML or any other) if this too complicated layer of interaction and add logic to build and decode what the message holds (analogous to the map solution but more generic across application layers). But I don't think this is what he wants.