Question

我想将一个 unsigned char [32] 数组转换为一个 4 元素的 uint64_t 数组。

我对 C++ 编码还很陌生，我真的很困惑。

unsigned char in_put [32] = { 1a, 2a, 3a, 4a, 5a, 6a, 7a, 8a, 1b, 2b, 3b, 4b, 5b, 6b, 7b, 8b, 1c, 2c, 3c, 4c, 5c, 6c, 7c, 8c, 1d, 2d, 3d, 4d, 5d, 6d, 7d, 8d }

我希望得到

uint64_t out_put [4] = { 0x1d2d3d4d5d6d7d8d, 0x1c2c3c4c5c6c7c8c, 0x1b2b3b4b5b6b7b8b, 0x1a2a3a4a5a6a7a8a }

最快、最便携的方式是什么？

Answer 1

我会写一个简单的函数：

inline uint64_t fourCh2uint64 (const unsigned char charArr[4]) {
    return  uint64_t(charArr[6]) << 56 | uint64_t (charArr[7]) << 48 |
            uint64_t(charArr[4]) << 40 | uint64_t (charArr[5]) << 32 |
            uint64_t(charArr[2]) << 24 | uint64_t (charArr[3]) << 16 |
            uint64_t(charArr[0]) << 8  | uint64_t (charArr[1]);
}

这是针对单个 uint64。对于其中 4 个，您可以使用：

char chArr[32] = {...}
uint64_t uintArr[4];
uintArr[0] = fourCh2uint64 (chArr);
uintArr[1] = fourCh2uint64 (chArr + 8);
uintArr[2] = fourCh2uint64 (chArr + 16);
uintArr[3] = fourCh2uint64 (chArr + 24);

这是整个程序：

#include <iostream>

inline uint64_t fourCh2uint64 (const unsigned char[4]);

int main (void) {
    unsigned char chArr [32] = {
        0x1a, 0x2a, 0x3a, 0x4a, 0x5a, 0x06a, 0x7a, 0x8a, 
            0x1b, 0x2b, 0x3b, 0x4b, 0x5b, 0x6b, 0x7b, 0x8b, 
                0x1c, 0x2c, 0x3c, 0x4c, 0x5c, 0x6c, 0x7c, 0x8c, 
                    0x1d, 0x2d, 0x3d, 0x4d, 0x5d, 0x6d, 0x7d, 0x8d
    };

    uint64_t uintArr[4];
    uintArr[0] = fourCh2uint64 (chArr);
    uintArr[1] = fourCh2uint64 (chArr + 8);
    uintArr[2] = fourCh2uint64 (chArr + 16);
    uintArr[3] = fourCh2uint64 (chArr + 24);

    std::cout << std::hex << uintArr[0] << " " << uintArr[1] << " ";
    std::cout << std::hex << uintArr[2] << " " << uintArr[3] << "\n";
                                                                                                                                                                                                                                                                                                                              
    return 0;
}

inline uint64_t fourCh2uint64 (const unsigned char charArr[4]) {
    return  uint64_t(charArr[0]) << 56 | uint64_t (charArr[1]) << 48 |
            uint64_t(charArr[2]) << 40 | uint64_t (charArr[3]) << 32 |
            uint64_t(charArr[4]) << 24 | uint64_t (charArr[5]) << 16 |
            uint64_t(charArr[6]) << 8  | uint64_t (charArr[7]);
}

和输出：

1a2a3a4a5a6a7a8a 1b2b3b4b5b6b7b8b 1c2c3c4c5c6c7c8c 1d2d3d4d5d6d7d8d

编辑：避免 UB 换档更新我的功能

将 char 数组转换为 uint64_t 数组

1 个答案: