在類中的const基本有三種用法
const int func(); // 返回值是const類型
int func(const int); // 參數爲const類型
int func(int )const; // 爲const類型的成員函數，只能調用類中const類型的變量；
另外，當類的實例是const類型時，也只能調用類中的const成員函數，且只有類的成員函數才能被修飾爲const類型；
//Point.h
#include <iostream>
using namespace std;
class Point{
private:
int x,y;
public:
Point(int a,int b){
x=a;y=b;
cout<<"Point constructor is called !\n";
};
~Point(){
cout<<"Point destructor is called !\n";
}
public:
const int getX(){
return x;
}
const int getY(){
return y;
}
public:
void setX(const int a,int b) {
x=a;y=b;
}
public:
void printPoint() const{
cout<<"const type\n";
cout<<"x="<<x<<",y="<<y<<endl;
}
void printPoint(){
cout<<"non const type\n";
cout<<"x="<<x<<",y="<<y<<endl;
}
};//main.cpp
#include <iostream>
#include "Point.h"
int main(int argc, const char * argv[])
{
// insert code here...
Point p(10,20);
Point const p1(30,40);
p1.printPoint();
p.printPoint();
//std::cout << "Hello, World!\n";
return 0;
}cout:
Point constructor is called !
Point constructor is called !
const type
x=30,y=40
not const type
x=10,y=20
Point destructor is called !
Point destructor is called !
Program ended with exit code: 0
將類中的
void printPoint()
函數刪除時則輸出：
Point constructor is called !
Point constructor is called !
const type
x=30,y=40
const type
x=10,y=20
Point destructor is called !
Point destructor is called !
Program ended with exit code: 0
所以類中的非 const成員函數也可調用const類型成員函數。