float_t有什么意义，什么时候应该使用？ [英] What's the point of float_t and when should it be used?
问题描述
我正在使用一个正在使用旧版GCC的客户端（3.2.3是准确的），但是想要升级，一个被认为是升级到较新版本的绊脚石的原因是大小差异的类型 float_t 其中，肯定是正确的：
I'm working with a client who is using an old version of GCC (3.2.3 to be precise) but wants to upgrade and one reason that's been given as stumbling block to upgrading to a newer version is differences in the size of type float_t which, sure enough is correct:
在GCC 3.2.3
sizeof(float_t) = 12
sizeof(float) = 4
sizeof(double_t) = 12
sizeof(double) = 8
GCC 4.1.2
sizeof(float_t) = 4
sizeof(float) = 4
sizeof(double_t) = 8
sizeof(double) = 8
但是这个区别的原因是什么？为什么大小变小，何时应该不应该使用 float_t 或 double_t ？
but what's the reason for this difference? Why did the size get smaller and when should and shouldn't you use float_t or double_t ?
推荐答案
float_t的原因是对于某些处理器和使用较大类型的编译器float double可以更有效，所以float_t允许编译器使用更大的类型而不是float。
The reason for float_t is that for some processors and compilers using a larger type e.g. long double for float could be more efficient and so the float_t allows the compiler to use the larger type instead of float.
因此在OPs的情况下使用float_t大小的变化是标准允许的。如果原始代码想要使用较小的浮点数，那么应该使用float。
thus in the OPs case using float_t the change in size is what the standard allows for. If the original code wanted to use the smaller float sizes it should be using float.
例如类型定义
float_t和double_t在
< math.h>中定义）旨在允许
有效使用具有
的架构更高效，更宽的格式。附件
for example the type definitions float_t and double_t (defined in <math.h>), are intended to allow effective use of architectures with more efficient, wider formats. Annexes
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