C++ : call another method for default method argument

Question

我正在项目中使用 Settings 类的默认参数，这样我声明的方法就会少一些。

例如，我声明了以下方法:

class Settings
{
    // [..]

    int getCurrentUserID(); // returns current user id

    // you specify the user id
    int setSetting( int value, int user_id ); 
    // no user specified, use the current one, overloads the previous when called
    // with only 1 argument
    int setSetting( int value ); 
}

我想要的是这个简化版本:

class Settings
{
    // [..]

    int getCurrentUserID(); // returns current user id

    // automatically selects the current user if no ID is provided
    int setSetting( int value, int user_id = getCurrentUserID() ); 
}

但是我在编译时收到此错误:

cannot call member function ‘int Settings::getCurrentUserID()’ without object

我如何告诉编译器使用Setting对象的当前实例(可通过this获得)来获取默认值？ 顺便问一下，这是授权的吗？

Answer 1

你有两个不错的选择。首先，假设 -1 不是合法的 user_id:

class Settings
{
    // [..]

    int getCurrentUserID(); // returns current user id

    // automatically selects the current user if no ID is provided
    int setSetting( int value, int user_id = -1); 
};

int Settings::setSetting( int value, int user_id )
{
    if(user_id == -1) user_id = getCurrentUserID();
 ...

或者:

class Settings
{
    // [..]

    int getCurrentUserID(); // returns current user id

    int setSetting( int value ) { return setSetting(value, getCurrentUserID() ); }

    int setSetting( int value, int user_id ); 
};