C中的2个字符 [英] 2 Chars to Short in C

问题描述

我有2个字符.

Char 128 和Char 2 .

Char 128 and Char 2.

如何将这些字符转换为C语言中的短 640 ?

How do I turn these chars into the Short 640 in C?

我尝试过

unsigned short getShort(unsigned char* array, int offset)
{
    short returnVal;
    char* a = slice(array, offset, offset+2);
    memcpy(&returnVal, a, 2);
    free(a);
    return returnVal;
}

但这没用，只是将其显示为 128 .首选方法是什么?

But that didn't work, it just displays it as 128. What's the preferred method?

推荐答案

我发现接受的答案几乎是正确的，除了我遇到一个错误，有时结果的最高字节为 0xff ...

I found that the accepted answer was nearly correct, except i'd run into a bug where sometimes the top byte of the result would be 0xff...

我意识到这是由于C符号扩展引起的.如果第二个字符为> = 0x80 ，则将 0x80 转换为短字符将变为 0xff80 .对任何内容执行 0xff80 的或"会导致最高字节保留为 0xff .

I realized this was because of C sign extension. if the second char is >= 0x80, then converting 0x80 to a short becomes 0xff80. Performing an 'or' of 0xff80 with anything results in the top byte remaining 0xff.

以下解决方案通过在b的隐式转换为short的过程中将b的高位字节清零来避免该问题.

The following solution avoids the issue by zeroing out the top byte of b during its implicit conversion to a short.

short c = (((short)a) << 8) | (0x00ff & b);

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