为什么在我的64位计算机上double和long double完全相同? [英] Why are double and long double completely the same on my 64 bit machine?

问题描述

对于初学者来说，这个问题听起来很像，但是当我发现自己以为是初学者或者我的伴侣缺少某些东西时:

This question may sound like for beginners, however when I found that out I thought I'm either a beginner or my comp is missing something:

int main()
{
    cout << sizeof(double) << endl;
    cout << sizeof(long double) << endl;

    cout << DBL_DIG << endl;
    cout << LDBL_DIG << endl;

    return 0;
}

程序输出:

8

8

15

15

我认为 long double 是10个字节，具有18个十进制数字，而 double 是8个字节，具有15个数字，但是似乎我错了.

I thought long double is 10 bytes and has 18 decimal digits while double is 8 bytes and has 15 digits but it seems I was wrong.

为什么会这样?

在64位计算机上使用MSVC 2010.

Using MSVC 2010 on 64bit machine.

推荐答案

在MSVC ++中， long double 是 double 的同义词.显然，这是为了利用仅限于64位操作的SSE/SSE2/SSE3指令集.

In MSVC++, long double is a synonym for double as you've found out. Apparently this is to take advantage of SSE/SSE2/SSE3 instruction sets which are limited to 64-bit operations.

另请参见此处.

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