Default template parameter in constructor

Question

So I have this piece of code and out of convenience I want the default parameter for its constructor be of the int kind and 0. (I have more parameters in a class of my project and one of them is optional and I don't want to write the constructor twice because its big)

class mama{
    public:
    template<typename x> mama(x i=int(0)){}
};

int main(){
    mama x;
}

This doesn't work because it says it can't find the constructor so is there another way I can do this?

error: no matching function for call to ‘mama::mama()'
note: candidates are: mama::mama(const mama&)

Answer 1

Refactor your constructor into a private initialization function and wrapper constructors, then add a default, like so:

class mama {
  private:
    template<typename x> void init(x i) { /* ... */ }
  public:
    template<typename x> mama(x i) { init(i); }
    mama() { init((int)0); }
};

Answer 2

Note that default template parameters are not allowed for function templates. Why not create a class template?

template <class T=int>
class mama{
    public:
    mama<T>(T i=0){}
};

int main(){
    mama<> x; // no argument based template parameter deduction possible
}

Answer 3

Default value works just like overload, so...

class mama{
public:
    template<typename x> mama(x i){}
    mama(int i = 0) {}
};

When you create mama with no argument, the construct with default int is matched before any templated constructor.