C ++同样的变量作为int和float [英] C++ same variable act as int and float

问题描述

我有情况，我需要保持值float以及int。所以尝试像下面。但没有帮助。可以帮助任何人吗？

I have on situation, where i need to keep the value float as well as int. so tried like below. but no help. can any one help on this?

union Val {
        int a;
        float b;
    };

    Val p;
    p.b = 45.56;

    int k = p.a; // i want k should be 45;

推荐答案

我看到您说：

我不想每次将它从float转换为int [sic]

i dont want each time it to be converted from float to int [sic]

可以使用用户定义的转化来完成此操作。

To do that you could use user-defined conversions to accomplish this.

所以你的结构如下：

class Val {
    int a;
    float b;
public:
    Val& operator= (const int _a) {a = _a; b = _a + fmod(b, 1.0F); return *this;}
    Val& operator= (const float _b) {b = _b; a = trunc(_b); return *this;}
    operator int() {return a;}
    operator float() {return b;}
};

请注意，你真正想要使用的只是一个 float 与 static_cast< int> 对于 static_cast ：

Please note that what you really want to use is simply a float with static_cast<int> For astatic_cast:

以确保正在转换的对象实际上是目标类型的完整对象。因此，由程序员确保转换是安全的。另一方面，它不会产生 dynamic_cast 的类型安全检查的开销。

No checks are performed during runtime to guarantee that the object being converted is in fact a full object of the destination type. Therefore, it is up to the programmer to ensure that the conversion is safe. On the other side, it does not incur the overhead of the type-safety checks of dynamic_cast.

我在这里提供了使用 Val 的示例： http://ideone.com/XUesib ，但您可以完成与 float foo 完全相同的事情：

I've provided an example of using Val here: http://ideone.com/XUesib but you could accomplish the exact same thing given float foo like this:

foo = 1.3F;
cout << static_cast<int>(foo) << endl << foo << endl;
foo = 13 + fmod(foo, 1.0F);
cout << static_cast<int>(foo) << endl << foo << endl;

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