调用函数时首选错误的参数转换

问题描述

我正在 MS Visual C++ 6.0 下编写程序(是的，我知道它很古老，不，我无能为力升级).我看到了一些我认为非常奇怪的行为.我有一个包含两个构造函数的类，定义如下:

I'm writing a program under MS Visual C++ 6.0 (yes, I know it's ancient, no there's nothing I can do to upgrade). I'm seeing some behavior that I think is really weird. I have a class with two constructors defined like this:

class MyClass
{
public:
    explicit MyClass(bool bAbsolute = true, bool bLocation = false) : m_bAbsolute(bAbsolute), m_bLocation(bLocation) { ; }
    MyClass(const RWCString& strPath, bool bLocation = false);

private:
    bool m_bAbsolute;
    bool m_bLocation;
};

当我使用以下语法实例化此类的实例时:MyClass("blah")，它调用第一个构造函数.正如您所看到的，我向它添加了 explicit 关键字，希望它不会这样做……没有骰子.它似乎更喜欢从 const char * 到 bool 的转换，而不是到 RWCString 的转换，后者有一个接受 const 字符 *.它为什么这样做?我认为，如果有两种可能的选择，它会说这是模棱两可的.我能做些什么来防止它这样做?如果可能的话，我想避免将 strPath 参数显式转换为 RWCString，因为它将与文字一起使用很多，而且很多额外的输入(加上一个非常容易犯的错误).

When I instantiate an instance of this class with this syntax: MyClass("blah"), it calls the first constructor. As you can see, I added the explicit keyword to it in the hopes that it wouldn't do that... no dice. It would appear to prefer the conversion from const char * to bool over the conversion to RWCString, which has a copy constructor which takes a const char *. Why does it do this? I would assume that given two possible choices like this, it would say it's ambiguous. What can I do to prevent it from doing this? If at all possible, I'd like to avoid having to explicitly cast the strPath argument to an RWCString, as it's going to be used with literals a lot and that's a lot of extra typing (plus a really easy mistake to make).

推荐答案

显式在这里没有帮助，因为构造函数不是隐式转换的一部分，只是接收者.

Explicit will not help here as the constructor is not a part of the implicit conversion, just the recipient.

无法控制首选的转换顺序，但您可以添加第二个采用 const char* 的构造函数.例如:

There's no way to control the preferred order of conversions, but you could add a second constructor that took a const char*. E.g:

class MyClass
{
public:
    MyClass(bool bAbsolute = true, bool bLocation = false);
    MyClass(const RWCString& strPath, bool bLocation = false);
    MyClass(const char* strPath, bool bLocation = false);

private:
    bool m_bAbsolute;
    bool m_bLocation;
};

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