https://stackoverflow.com/a/3533692

这个挺有意思的,重写虚函数顺便重写了默认参数的值
结果调用的时候默认参数是编译的时候定的,函数是运行的时候定的
一不留神可能又是一个坑啊

#include <string>
#include <sstream>
#include <iostream>
#include <iomanip>


using std::stringstream;
using std::string;
using std::cout;
using std::endl;

struct Base { virtual string Speak(int n = 42); };
struct Der : public Base { string Speak(int n = 84); };

string Base::Speak(int n)
{
    stringstream ss;
    ss << "Base " << n;
    return ss.str();
}

string Der::Speak(int n)
{
    stringstream ss;
    ss << "Der " << n;
    return ss.str();
}

int main()
{
    Base b1;
    Der d1;

    Base *pb1 = &b1, *pb2 = &d1;
    Der *pd1 = &d1;
    cout << pb1->Speak() << "\n"    // Base 42
        << pb2->Speak() << "\n"     // Der 42
        << pd1->Speak() << "\n"     // Der 84
        << endl;
}
--
FROM 171.83.7.*