我使用的平台是小端模式：
声明这样一个联合体：
[mw_shl_code=c,true]typedef union { u32 dword; u16 word[2]; u8 byte[4]; }u32val;[/mw_shl_code]
[mw_shl_code=c,true]int main() { u8 volatile a,b,c,d; u16 volatile e,f; u32val volatile u32j,*u32p; u32 volatile g,h,i,j,k; u32p = &u32j; u32p->dword = 0x12345678; a = u32p->byte[0]; b = u32p->byte[1]; c = u32p->byte[2]; d = u32p->byte[3]; e = u32p->word[0]; f = u32p->word[1]; g = (u32)u32p; h = (u32)(u32p->byte); i = (u32)(u32p->word); j = (u32)&(u32p->byte[1]); k = (u32)&(u32p->word[1]); } [/mw_shl_code]
可以省去移位操作，来进行字节拼接成字。
比如：地址的拼接与拆分。 例如这样一个函数： [mw_shl_code=c,true]typedef union { u32 DWord; u16 Word[2]; u8 Byte[4]; }UINT32_VAL; u32 SPIReadDWord(u16 Address) { UINT32_VAL dwResult; UINT16_VAL wAddr; wAddr.Word = Address; SPI_SEL_ENABLE; SPI2_ReadWriteByte(CMD_SERIAL_READ); SPI2_ReadWriteByte(wAddr.Byte[0]); SPI2_ReadWriteByte(wAddr.Byte[1]); dwResult.Byte[0] = SPI2_ReadWriteByte(0xff); dwResult.Byte[1] = SPI2_ReadWriteByte(0xff); dwResult.Byte[2] = SPI2_ReadWriteByte(0xff); dwResult.Byte[3] = SPI2_ReadWriteByte(0xff); SPI_SEL_DISABLE; return dwResult.DWord; } [/mw_shl_code]
好处不言而喻。但是缺点就是，注意处理器的大小端模式。