c语言小端转大端

//小端转大端
int little2big(int le) {

    return (le & 0xff) << 24 
            | (le & 0xff00) << 8 
            | (le & 0xff0000) >> 8 
            | (le >> 24) & 0xff;
}

//大端转小端
int big2little(int be)
{
    return ((be >> 24) &0xff ) 
        | ((be >> 8) & 0xFF00) 
        | ((be << 8) & 0xFF0000) 
        | ((be << 24));    
}

short大小端转换

小端转大端
short little2bigs(short num)
{
    short swapped = (num >> 8) | (num << 8);
    return swapped;
}

大端转小端
short big2littles(short be)
{
    short swapped = (be << 8) | (be >> 8);
    return swapped;
}

32大端转小端原理

swapped = ((num>>24)&0xff) | // move byte 3 to byte 0
                    ((num<<8)&0xff0000) | // move byte 1 to byte 2
                    ((num>>8)&0xff00) | // move byte 2 to byte 1
                    ((num<<24)&0xff000000); // byte 0 to byte 3

内置函数（传入大端转小端，小端转大端，以下同理）

16位无符号，大小端转换

unsigned short _byteswap_ushort(unsigned short value);

32位无符号，大小端转换

unsigned long _byteswap_ulong(unsigned long value);

64位无符号，大小端转换

unsigned __int64 _byteswap_uint64(unsigned __int64 value);

参考来源：

convert big endian to little endian in C [without using provided func]

 Converting Little Endian to Big Endian

How do I convert between big-endian and little-endian values in C++?