Question

我有一个类别,只有数据成员,即32个点名未经签名的分类。也就是说,这一类人认为:

class A {
protected:
    unsigned int bits;
    /* ... some methods ... */
public:
    /* ... some methods ... */
};

但是,我也希望能够从32个没有签名的ger户中暗地皈依。因此,我在一份影印构件中加上了一台投稿人。

class A {
protected:
    unsigned int bits;
    /* ... some methods ... */
public:
    A(): bits(0) {} // default constructor
    A(const unsigned int i): bits(i) {} // convert from unsigned int to A
    operator unsigned int() { return bits; } // convert from A to unsigned int
    /* ... some methods ... */
};

例如,我现在可以做以下工作:

int main () {
    // default constructor
    A a0 = A();
    // convert from unsigned int
    A a1 = 1 + 2;
    // conversions between the two types:
    unsigned int result = (a0 & a1 + 5) / 2;
}

然而,我却在努力使其工作达到<条形状>。尤其是,以下工作:

int main () {
    const A a = 5;      // works
    unsigned int i = a; // compiletime error
}

It says "No suitable conversion function from const A to unsigned int exists.". I m using Visual Studio 2010 with the default compiler as provided by microsoft.

我需要创造哪些转换功能,以便适当开展工作?

Answer 1

Declare the conversion operator const:

operator unsigned int() const { return bits; }

洞穴:合法皈依业者几乎总是不好。危险通常远远大于要求履行老旧成员职责的轻微不便:

unsigned int asInt() const { return bits; }
⋮
unsigned int i = a.asInt();

The ultimate solution, if you have C++11, is to declare an explicit conversion operator:

explicit operator unsigned int() const { return bits; }
⋮
unsigned int i = static_cast<int>(a);

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