c++ - 错误：为参数 1 提供了默认参数

Question

我收到以下代码的错误消息：

class Money {
public:
    Money(float amount, int moneyType);
    string asString(bool shortVersion=true);
private:
    float amount;
    int moneyType;
};

首先，我认为默认参数不允许作为 C++ 中的第一个参数，但它是允许的。

Answer 1

您可能正在重新定义函数实现中的默认参数。它应该只在函数声明中定义。

//bad (this won't compile)
string Money::asString(bool shortVersion=true){
}

//good (The default parameter is commented out, but you can remove it totally)
string Money::asString(bool shortVersion /*=true*/){
}

//also fine, but maybe less clear as the commented out default parameter is removed
string Money::asString(bool shortVersion){
}

Answer 2

I made a similar error recently. this is how I resolved it.

when having a function prototype and definition. the default parameter is not specified in the definition.

eg:

int addto(int x, int y = 4);

int main(int argc, char** argv) {
    int res = addto(5);
}

int addto(int x, int y) {
    return x + y;
}