Question

这刚刚变成了一场火焰战。如果我不明白，我会在以后再问这个问题。

在函数内部更改值，但一旦函数结束，值将返回到最初设置的值。

class inventory
 {
private:
struct instock {

    double everything[4]; //Gets set to 0-3. Then user changes values.

};

public:
instock stock;
void changegas(double userinput);
void stocking(); //populates the array
void output();  //outputs the array
};

void inventory::stocking(){
for(int i=0; i<4; i++){
    stock.everything[i]=i;
 }
}

void inventory::changegas(double input){
double a;
a = input;
stock.everything[0] += a;
std::cout << "Gas remaining: " << stock.everything[0];
}

void inventory::output(){
std::cout << std::endl;
    for(int i=0; i<4; i++){
 std::cout << stock.everything[i];
 }
}

void inventory::changegas(double input){
double a;
a = input;
stock.everything[0] += a;
std::cout << "Gas remaining: " << stock.everything[0];
}

我该怎么做才能让这个函数永久地改变存储在一切中的数组的值？

   int main()
{


backroom.stocking();

int choice;

cout << "What would you like to change? \n1.)Gas\n2.)Tires\n3.)Soda\n4.)Snacks"<<endl;
cin >> choice;
menu(choice, backroom);
backroom.output();




return 0;
}

void menu(int zed, inventory a){
 int z = zed;
 int c = 0;
switch (z){//start switch

case 1:
    cout << "Enter the amount of Gas you want to change: ";
    cin >> c;
    a.changegas(c);
    break;
case 2:
    cout << "Enter the amount of Tires you want to change: ";
    cin >> c;
    a.changetires(c);
    break;
case 3:
    cout << "Enter the amount of Soda you want to change: ";
    cin >> c;
    a.changesoda(c);
    break;
case 4:
    cout << "Enter the amount of Snacks you want to change: ";
    cin >> c;
    a.changesnacks(c);
    break;

    break;
}//endswitch

}// end funct

我知道数组是通过引用传递的，所以我认为这样可以正常工作。但显然我并没有正确理解。目前仍在学习语言。也许我没有正确地传递数组？

Answer 1

你按价值通过了后台。您需要更改menu()以接收库存参考或库存指针，最好是前者。这是因为当您按值传递类对象时，整个对象将被复制到被调用函数的本地新实例，并且对该实例所做的任何更改都不会影响原始副本。

这应该有效：

void menu(int zed, inventory& a) {
    int z = zed; //you don't need this by the way
    int c = 0;

    switch (z){//start switch
    case 1:
        cout << "Enter the amount of Gas you want to change: ";
        cin >> c;
        a.changegas(c);
        break;
    case 2:
        cout << "Enter the amount of Tires you want to change: ";
        cin >> c;
        a.changetires(c);
        break;
    case 3:
        cout << "Enter the amount of Soda you want to change: ";
        cin >> c;
        a.changesoda(c);
        break;
    case 4:
        cout << "Enter the amount of Snacks you want to change: ";
        cin >> c;
        a.changesnacks(c);
        break;
    }
}

如何更改私有类内部结构中的数组？（c ++）

1 个答案: