类连续数据 [英] Class contiguous data

问题描述

我有一个C ++类，它有四个私有浮点和一堆非静态公共函数，对这些数据进行操作。

I have a C++ class which has four private floats and a bunch of nonstatic public functions that operate on this data.

是保证还是可能所以，四个浮点是连续的，没有填充。这将使类的大小为四个浮点，它的地址将是第一个浮点的。

Is it guaranteed, or possible to make it so, that the four floats are contiguous and there is no padding. This would make the class the size of four floats, and it's address would be that of the first float.

推荐答案

您的编译器。

您可以使用 #pragma pack（1） MSVC 和 gcc 或 #pragma pack 1 aCC 。

例如，假设 MSVC / gcc ：

#pragma pack(1)
class FourFloats
{
    float f1, f2, f3, f4;
};

或更好：

#pragma pack(push, 1)
class FourFloats
{
    float f1, f2, f3, f4;
};
#pragma pack(pop)

基本上禁用填充并保证 floats 是连续的。但是，为了确保类的大小实际上是 4 * sizeof（float），它不能有 vtbl ，表示虚拟成员是禁用的。

That basically disables padding and guarantees that the floats are contiguous. However, to ensure that the size of your class is actually 4 * sizeof(float), it must not have a vtbl, which means virtual members are off-limits.

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