C ++声明独立于平台的32位浮点数 [英] C++ declare platform independent 32-bit float

问题描述

有没有一种方法可以在C ++中声明32位浮点值-确保无论平台/编译器如何，它始终为32位？

Is there a way to declare 32-bit floating point value in C++ - ensuring that it will always be 32 bits regardless of platform/compiler?

我可以这样做对于这样的整数：

I can do that for integers like that:

#include <stdint.h>

uint32_t var;  //32 bit unsigned integer
uint64_t var1; //64 bit unsigned integer

是否可以对浮点数执行类似的操作？据我所知，

is there a way to do something like that for floats? As far as I know,

float var; //Usually is 32 bit, but NOT GUARANTEED to be 32 bit

是特定于实现的，并且不是一定是32位..（如果我错了，请纠正我）。

is implementation specific, and is not necessarily 32 bit.. (Correct me if I am wrong).

我正在使用qt，因此，如果有使用它的解决方案，我将接受它-我找不到类似quint16的float（qreal会根据平台更改大小） ）。

I am using qt, so if there is any solution using it I would accept it - I couldn't find anything like quint16 for floats (qreal changes size depending on platform).

推荐答案

您正在使用Qt。

据我所知，在支持Qt的所有平台上，键入 float 是32位IEEE。

As far as I know, on all platforms where Qt is supported, type float is 32-bit IEEE.

如果有人决定将Qt移植到具有64位的Cray向量机上位 float ，无论如何您都不会拥有32位浮点类型（除非您自己在软件中实现它，但我不知道如何实现）会很有用）。

If somebody decides to port Qt to, say, a Cray vector machine with 64-bit float, you're not going to have a 32-bit floating-point type anyway (unless you implement it yourself in software, but I don't see how that would be useful).

没有< stdfloat.h> / < ; cstdfloat> 对应于< stdint.h> / < cstdint> 。 C和C ++提供 float ， double 和 long double ，并且对它们施加了最低要求，但是并没有给您提供要求任何特定大小的浮点类型的方法。

There is no <stdfloat.h> / <cstdfloat> corresponding to <stdint.h> / <cstdint>. C and C++ provide float, double, and long double, and imposes minimal requirements on them, but doesn't give you a way to ask for a floating-point type of any specific size.

您最好的选择可能是在 main 或保证在程序启动期间调用的某些函数中添加以下内容：

Your best bet is probably to add something like this in main, or in some function that's guaranteed to be called during program startup:

assert(CHAR_BIT * sizeof (float) == 32);

也许还有 CHAR_BIT == 8

assert 不太可能触发，并且如果触发， ，您会遇到更大的问题。

It's unlikely that the assert will ever fire -- and if it does, you've got bigger problems.

您可能想重新考虑是否真的需要32位浮点类型。如果您的代码在具有64位 float 的系统上运行，那怎么会不能满足您的要求？

You might want to reconsider whether you really need a 32-bit floating type. If your code were running on a system with 64-bit float, how would that fail to meet your requirements?

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