#include<stdio.h>
#include <string.h>
typedef unsigned char  uint8_t;
typedef unsigned short uint16_t;
typedef unsigned int   uint32_t;


void u8_to_u32(unsigned char* u8,unsigned int *u32)
{
	if(0)
		*u32 = (u8[0]<<24)|(u8[1]<<16)|(u8[2]<<8)|u8[3];
	else
		*u32 = (u8[3]<<24)|(u8[2]<<16)|(u8[1]<<8)|u8[0];


}
int main(void)
{
unsigned int  u32 = 0;
unsigned char tem[4]={0x01,0X02,0X03,0X04} ;
memcpy((uint8_t*)&u32,tem,sizeof(tem));
printf("%04X\n",u32); 

u8_to_u32(tem,&u32);
printf("%04X\n",u32); 
}
//04030201
//04030201  如果上面修改if(1)就反過來