用 4 个复合字节构建一个 32 位浮点数
我正在尝试用它的 4 个复合字节构建一个 32 位浮点数.有没有比使用以下方法更好(或更便携)的方法?
I'm trying to build a 32-bit float out of its 4 composite bytes. Is there a better (or more portable) way to do this than with the following method?
#include <iostream>
typedef unsigned char uchar;
float bytesToFloat(uchar b0, uchar b1, uchar b2, uchar b3)
{
float output;
*((uchar*)(&output) + 3) = b0;
*((uchar*)(&output) + 2) = b1;
*((uchar*)(&output) + 1) = b2;
*((uchar*)(&output) + 0) = b3;
return output;
}
int main()
{
std::cout << bytesToFloat(0x3e, 0xaa, 0xaa, 0xab) << std::endl; // 1.0 / 3.0
std::cout << bytesToFloat(0x7f, 0x7f, 0xff, 0xff) << std::endl; // 3.4028234 × 10^38 (max single precision)
return 0;
}
推荐答案
你可以使用 memcpy
(结果)
float f;
uchar b[] = {b3, b2, b1, b0};
memcpy(&f, &b, sizeof(f));
return f;
或联合*(结果)
union {
float f;
uchar b[4];
} u;
u.b[3] = b0;
u.b[2] = b1;
u.b[1] = b2;
u.b[0] = b3;
return u.f;
但这并不比你的代码更便携,因为不能保证平台是 little-endian 或 float
使用 IEEE binary32 甚至 sizeof(float) ==4代码>.
But this is no more portable than your code, since there is no guarantee that the platform is little-endian or the float
is using IEEE binary32 or even sizeof(float) == 4
.
(注意*:如 @James,技术上不允许在标准 (C++ §[class.union]/1) 中访问联合成员 uf
.)
(Note*: As explained by @James, it is technically not allowed in the standard (C++ §[class.union]/1) to access the union member u.f
.)
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