我如何把一个无符号的字符数组为unsigned long long？ [英] how do i convert an unsigned char array into an unsigned long long?

问题描述

让我们说，我有8个无符号的字符，我要转换为unsigned long long。

let's say that i have 8 unsigned char, that i want to convert to an unsigned long long.

例如，如果所有字符都等于为0xFF，无符号长长将等于至0xFFFFFFFFFFFFFFFF。

for example, if all char are equals to 0xFF, the unsigned long long would be equal to 0xFFFFFFFFFFFFFFFF.

什么是最有效的方式来做到这一点与C或C ++？

what's the most efficient way to do that with C or C++?

推荐答案

的memcpy的相反，您可以直接分配位

Instead of memcpy, you can directly assign the bits

  unsigned char buffer[8] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };
  unsigned long long l = 0;
  for (int i = 0; i < 8; ++i) {
    l = l | ((unsigned long long)buffer[i] << (8 * i));
  }

我相信这是免疫字节序。

I believe this is immune to endianness.

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