Thread: No Matching Function Call for Constructor

'am using maps for the first time. Can not figure out why the

Code:

o_f  _sin(&d_sin);

is not working.

Code:

#include<map>
#include<cmath>
class o_f        //Operator Functions 
{
    public:
    double (*func)(double);
    o_f(double (*fun)(double))      {func = fun;};
};
double d_sin(double x)               //double_sin
{
    return sin(x);
}
int main()
{
    std::map<int,o_f> m;
    o_f  _sin(&d_sin);
    m[1]=_sin;

    return 0;
}

The lack of default contructor has nothing to do with knowing the size of the class.

The problem is with how operator[] works for map. If the item is not present in the map, it is first inserted using the default constructor and then a reference to the new item is returned. It's only to that reference that you are assigning _sin to.

If you don't want to add a default constructor to the class, you can still use map, but not operator[].

To insert items you can use:

Code:

m.insert(std::make_pair(1, _sin));

and to look it up, you'd need the find member function.