在cpp中声明的C ++访问常量值

Question

I have a main method in my main.cpp that I would like to display the value of a constant int I have declared.

I added a DeclareConstant class.

Here is my DelcareConstant.h

#pragma once
class DeclareConstant
    {

 public:
     const int x;
     Part1(void);
     Part1(int x);
     ~Part1(void);
     double getX(){return x;}
 };

And source

#include "Part1.h"

Part1::Part1() : x(55){
}

How can I access X so I can display it in my main method? I need to check if I'm even initializing it correctly.

Answer 1

You can access x through getter function getX() , for example:

DeclareConstant dc;
std::cout << dc.getX() << std::endl;

Or

DeclareConstant dc;
std::cout << dc.x << std::endl;

However, you should define your getX like this:

class DeclareConstant
{

 public:
     int getX() const {return x;}

 private:
  const int x; 
 };

And please hide your class member.

Answer 2

You need an object or an instance of DeclareConstant to access the DeclareConstant 's x member.

DeclareConstant myConst;
std::cout << myConst.x << std::endl;   // Use x

But for your possible purpose and intentions you could make x as a static member .

class DeclareConstant {
public:
   static const int x = 55;
   // ...
}

You now don't need an instance to get the value of x :

std::cout << DeclareConstant::x << std::endl;   // Use x

Answer 3

If all your instances use the same constant value, you can make it static. This has a couple of advantages.

You can define it as below.

class Part1{

public: static const int x = 42; Part1(void); Part1(int x); ~Part1(void); double getX(){return x;} };

and access it simply as Part1::x . You should make getX static as well, then you can do Part1::getX() .

This will not work if each instance has its own const value.