从另一个参数的值设置默认参数值

Question

是否可以实现这样的功能，如果未指定，该参数的值将默认为另一个参数的值？

示例：

class Health
{
public:
    // If current is not specified, its value defaults to max's value
    Health(int max, int current = max) : max_(max), current_(current) { }
    int max_;
    int current_;
};

就像现在一样，我遇到了编译错误：

error: 'max' was not declared in this scope
Health(int max, int current = max) : max_(max), current_(current) { }
                              ^

Answer 1

您必须提供重载：

class Health
{
public:
    Health(int max, int current) : max_(max), current_(current) { }

    Health(int max) : max_(max), current_(max) {}
    // or `Health(int max) : Health(max, max) {}` since C++11

    int max_;
    int current_;
};

Answer 2

您可以将参数默认为不应接受的值，然后在初始化时使用 ? 运算符进行检查

class Health
{
public:
    // If current is not specified, its value defaults to max's value
    Health(int max, int current = 0) : max_(max), current_(current == 0 ? max : current) { }
    int max_;
    int current_;
};

从另一个参数的值设置默认参数值

Set default parameter value from another paramater's value

c++

parameters