c++ - 如何在C++中以大端方式移动位

Question

这是小端位移的代码，我想把它转换成大端位移。 请帮帮我。实际上这是使用小端移位的 LZW 解压缩代码。 但我想要大端代码

unsigned int input_code(FILE *input)
{
unsigned int val;
static int bitcount=0;
static unsigned long inbitbuf=0L;

  while (bitcount <= 24)
  {
      inbitbuf |=(unsigned long) getc(input) << (24-bitcount);
      bitcount += 8;
  }

  val=inbitbuf >> (32-BITS);
  inbitbuf <<= BITS;
  bitcount -= BITS;

  return(val);
}


void output_code(FILE *output,unsigned int code)
{
static int output_bit_count=0;
static unsigned long output_bit_buffer=0L;

output_bit_buffer |= (unsigned long) code << (32-BITS-output_bit_count);
output_bit_count += BITS;
while (output_bit_count >= 8)
{
    putc(output_bit_buffer >> 24,output);
    output_bit_buffer <<= 8;
    output_bit_count -= 8;
}
}

Answer 1

你可能想要类似的东西。

unsigned char raw[4];
unsigned int val;
if (4 != fread(raw, 1, 4, input)) {
  // error condition, return early or throw or something
}
val = static_cast<unsigned int>(data[3])
    | static_cast<unsigned int>(data[2]) << 8 
    | static_cast<unsigned int>(data[1]) << 16 
    | static_cast<unsigned int>(data[0]) << 24; 

如果您使用的是小字节序，则反转索引，一切都保持不变。

很好rant on endianness以及人们似乎编写的代码，如果您想要更多的话。