c++ - 如何知道是否传递了可选函数参数还是使用默认函数参数？

Question

这个问题已经有答案了:

Is it possible to know if the parameter was defaulted (3 个回答)

已关闭 7 年前。

void foo (  int arg1, int arg2)

foo(1)

foo(1,2)

我如何知道 int arg2 是否使用像第二个 foo 调用中那样传递的可选函数参数，或者像第一个 foo 中那样使用默认参数？

更新:

公开:

头文件

// Point 1
void fireworkShipment(stack<Firework*>&);
void sellFireworks(stack<Firework*>&, int quantity);

// Point 2
void metalShipment(stack<Metal>&);
~FireworkFactory();

// Point 3 for correctness, Point 4 for O(1) runtime
void sellFireworks(stack<Firework*>&, int quantity, Color color);
void sellFireworks(stack<Firework*>&, int quantity); //error here

cpp文件:

    void FireworkFactory::sellFireworks(stack<Firework*>& customerStack, int quantity, Color color){
    // TODO
    cout<< "which color: " << color << "\n";
    for (int i = 0; i< fireworkstorage.size(); i++) {
        if (fireworkstorage.front()->getColor() == color && quantity != 0) {
            customerStack.push(fireworkstorage.front());
            cout<< "Color: " <<fireworkstorage.front()->getColor() << "\n";
            fireworkstorage.pop();
            quantity--;
            cout<<  "Quantity: " <<quantity << "\n";
        } else {
            fireworkstorage.push(fireworkstorage.front());
            fireworkstorage.pop();
        }
    }    
}

void FireworkFactory::sellFireworks(stack<Firework*>& customerStack, int quantity){
    for (int i = 0; i<quantity; i++) {
        customerStack.push(fireworkstorage.front());
        fireworkstorage.pop();
    }
}

Answer 1

你不能。但是，您可以使用一个参数创建重载函数:

#include <iostream>

void awesome_function_with_default_parameters(int arg1, int arg2 = 42)
{
    std::cout << "Doing some awesome work with " << arg1 << " and " << arg2 << std::endl;
}

void foo(int arg1, int arg2)
{
    std::cout << "Both parameters passed" << std::endl;
    awesome_function_with_default_parameters(arg1, arg2);
}

void foo(int arg1)
{
    std::cout << "Only one parameter passed" << std::endl;
    awesome_function_with_default_parameters(arg1);
}

int main()
{
    foo(1);
    foo(1, 314);
    return 0;
}