C++隐式类型转换运算符operator type()用法详解

#include "algostuff.hpp"

class MeanValue{
private:
  long num;
  long sum;
public:
  MeanValue():num(0),sum(0){
  }

  void operator() (int elem){
    num++;
    sum += elem;
  }
  operator double(){
    return static_cast<double>(sum) / static_cast<double>(num);
  }
};

int main()
{
  std::vector<int> coll;
  INSERT_ELEMENTS(coll,1,8);
  double mv = for_each(coll.begin(),coll.end(),MeanValue()); //隐式类型转换 MeanValue转化为double
  std::cout<<"mean calue: "<< mv <<std::endl;
}

#include<iostream>
#include<string>
using namespace std;
 
class D{
public:
  D(double d):d_(d) {}
  operator int() const{
    std::cout<<"(int)d called!"<<std::endl;
    return static_cast<int>(d_);
  }
private:
  double d_;
};
 
int add(int a,int b){
  return a+b;
}
 
int main(){
  D d1=1.1;
  D d2=2.2;
  std::cout<<add(d1,d2)<<std::endl;
  system("pause");
  return 0;
}

#include<iostream>
class X;
class A
{
public:
  A(int num=0):dat(num) {}
  A(const X& rhs):dat(rhs) {}
  operator int() {return dat;}
private:
  int dat;
};
 
class X
{
public:
  X(int num=0):dat(num) {}
  operator int() {return dat;}
  operator A(){
    A temp=dat;
    return temp;
  }
private:
  int dat;
};
 
int main()
{
 X stuff=37;
 A more=0;
 int hold;
 hold=stuff;
 std::cout<<hold<<std::endl;
 more=stuff;
 std::cout<<more<<std::endl;
 return 0;
}