在名称空间中定义类的构造函数

Question

I am fairly new to C++ so this may be an easy one. I created a namespace and inside that namespace is a class. I cannot figure out how to define any of my class's constructors without receiving errors.

#include <iostream>

namespace bill {
    const char * null ="EMPTY";
    const int MAX_STACK_SIZE = 100;
    class myStackClass {
    private:
        int i;
    public:
        myStackClass();
        myStackClass(int[], int);
        int peek();
        int pop();
        int push(int insertMe);
        const char empty[5];
    };
}
using namespace bill;
bill::myStackClass::myStackClass() //bill::myStackClass() doesn't work either
    :
    i(0)
{ //error C2448: 'i' : function-style initializer appears to be a function definition
} //"bill::myStackClass::myStackClass()" provides no initializer for:
        const member "bill::myStackClass::empty"


bill::myStackClass::myStackClass(int[],int)
{ //error C2439: 'bill::myStackClass::empty' : member could not be initialized
} //"bill::myStackClass::myStackClass(int *, int)" provides no initializer for:
        const member "bill::myStackClass::empty"

int bill::myStackClass::peek() // I am able to call methods belonging to the class
{
}

I'm sorry if any of this information is cluttered and hard to read or just downright not helpful. I have been reading my textbook and googling errors for hours and would really appreciate some insight. Thank you.

Answer 1

It's a bit difficult to decipher what you're looking for, as your stack class isn't much of a stack. That said, just to get it to compile without warnings, you have to initialize your empty class member in the constructor initializer list, as you've declared it to be const.

eg if you have your constructors as:

bill::myStackClass::myStackClass()
  : i(0), empty {} 
{}

bill::myStackClass::myStackClass(int[],int) 
  : empty{}
{}

This will initialize your empty char array to be, well, empty. If you wanted it to contain something, then you could specify it in within the curly brackets, eg

bill::myStackClass::myStackClass()
  : i(0), empty {'H', 'E', 'L', 'L', 'O'} 
{ 
    std::cout << empty << std::endl;                                         
}

then creating an object of your class (via the no-arg constructor) will print HELLO

bill::myStackClass stk; //--> prints HELLO

I should also make note that the use of uniform initializers (the curly-braces) is a C++11 feature, so depending on your compiler, you might have to supply an extra flag (ie -std=c++11)

You don't need to say using namespace bill if you are already pre-pending bill:: to your method definitions (which in your posted code, you are). The using namespace bill makes it such that the bill namespace is searched when resolving your identifier names, but if you're explicitly stating them to be bill within the bill namespace (via the bill:: ), then this isn't needed.

Also, the default scoping for a class if private, so it's redundant to specify the first part of a classes members to be private like that.