Question

I have two different versions of the constructor for my “Policy” class. I can’t seem to pass a Policy object by reference when using one of the constructors, and I don’t understand why not.

Overloaded constructors:

Policy::Policy(int testing) { 
    initAge=160;    
    initState=1;    

    reset();        

    x[0]=4;
    x[1]=2;
    ub[0]=10;
    ub[1]=10;
    lb[0]=0;
    lb[1]=0;

}

Policy::Policy() {
    initAge=160;
    initState=1;

    reset();    

    x[FRQ]=4;
    x[BEG]=40*4;
    x[END]=75*4;
    for(int i=0; i<240; i++)
        x[2+i]=4.0;
    x[GS]=2;

    lb[0]=1;
    ub[0]=80;
    for(int i=1;i<3;i++) {
        lb[i]=160;
        ub[i]=400;
    }
    for(int i=3;i<243;i++) {
        lb[i]=1;
        ub[i]=16;
    }
    lb[243]=2;
    ub[243]=4;

} 

Here’s my code that gives the error.

void sampleMIXD(Constraints& space, Policy& p);

int main(int argc, char** argv) {

//  Policy policy(1); // Works
    Policy policy(); // Does not work

    Constraints space(2);

    sampleMIXD(space, policy);

    return 0;
}

Error message:

'../main.cpp:64: error: invalid initialization of non-const reference of type 'Policy' from a temporary of type 'Policy (*)()'
../MIXD.h:12: error: in passing argument 2 of 'void sampleMIXD(Constraints&, Policy&)'

If instead of Policy policy(); I compile with Policy policy(1);, then the compiler doesn’t complain. Please help! 🙂

Answer 1

Policy policy(); // Does not work

That’s the most vexing parse. Try

Policy policy;

Basically, the compiler treats your variant as a declaration of a function taking nothing and returning policy. It’s similar to

int rand();