How to pass optional parameter to a method in C++?

Question

How to pass optional parameters to a method in C++ ?

is there a way like in C# we can use this statement Func(identifier:value) which allow me to pass value to any parameter i want .... for example:

   //C# Code
   void func(int a=4,int b,int c)
    {
    int sum=a+b+c;
    Console.Write(sum);
    }
    void Main(){ func(b:5,c:6);}

Answer 1

In C++, default arguments have to go last, so you would write:

void func(int b, int c, int a=4)
{
    int sum = a+b+c;
    std::cout << sum;
}

int main() {
    func(5, 6); // b = 5, c = 6, a uses the default of 4
}

You cannot provide named parameters all the call site the way you can in C# or Python. There is a boost library to fake support for naming parameters, but I've never used it.

Answer 2

Yes, but, short answer is that a parameter with a default value cannot precede parameters which don't get defaults. So:

void func(int a=4,int b,int c) {} //doesn't work
void func(int b, int c, int a = 4){} //works

See http://en.cppreference.com/w/cpp/language/default_arguments for more information

Answer 3

Yes, but you can only do it to the rightmost elements. So you could write void func(int a, int b, int c=4) or void func(int a, int b=2, int c=4) or even void func(int a=1, int b=2, int c=4) , but not the example you gave.