C語言編程中的8位、16位、32位整數的分解與合併

在單片機的編程中對於8位、16位、32位整數的分解與合併用的比較多，今天作了簡要學習，後面還須要加以總結。

　　練習在VC++6.0編程環境中進行，源程序：
#include <stdio.h>
#include "string.h"

int main(int argc, char argv[])
{
unsigned int Data_Uint32=0x12345678;
unsigned short int Data_Uint16_1,Data_Uint16_2;
unsigned char Data_Uint8_1,Data_Uint8_2,Data_Uint8_3,Data_Uint8_4;
struct StructByte8{
unsigned char Byte01:1;
unsigned char Byte02:1;
unsigned char Byte03:1;
unsigned char Byte04:1;
unsigned char Byte05:1;
unsigned char Byte06:1;
unsigned char Byte07:1;
unsigned char Byte08:1;
} Test1;
unsigned char C1[]="A";
unsigned short int p16=(unsigned short int *)(&Data_Uint32);//定義16位的指針將32位地址強制轉爲16位，高位丟棄取低位
unsigned short int Data_Uint16_2p,Data_Uint16_1p;

printf("32位整數：0x%x\n",Data_Uint32);
  printf("-------------------經過指針運算-------------------\n");
  Data_Uint16_2p=*(unsigned short int *)p16;
  Data_Uint16_1p=*((unsigned short int *)p16+1);
  printf("轉換後的16位整數：0x%x,0x%x\n",Data_Uint16_1p,Data_Uint16_2p);

  Data_Uint8_1= *(unsigned char *)p16;
  Data_Uint8_2= *((unsigned char *)p16+1);
  Data_Uint8_3= *((unsigned char *)p16+2);
  Data_Uint8_4= *((unsigned char *)p16+3);
  printf("轉換後的8位整數：0x%x,0x%x,0x%x,0x%x\n",Data_Uint8_1,Data_Uint8_2,Data_Uint8_3,Data_Uint8_4);

  Data_Uint8_1=0;Data_Uint8_2=0;Data_Uint8_3=0;Data_Uint8_4=0;
  //直接根據指針取值
  //將32位的整數分解成兩個16位的整數,再取低位的16位
  //強制轉換，丟棄高位的16位
  //32位轉16位
  Data_Uint16_1=(unsigned short int)(Data_Uint32>>16);
  Data_Uint16_2=(unsigned short int)Data_Uint32;

  //32位轉8位
  Data_Uint8_1= (unsigned char)(Data_Uint32>>24);
  Data_Uint8_2= (unsigned char)(Data_Uint32>>16);
  Data_Uint8_3= (unsigned char)(Data_Uint32>>8);
  Data_Uint8_4= (unsigned char)Data_Uint32;

  printf("-------------------經過位運算-------------------\n");
  printf("轉換後的16位整數：0x%x,0x%x\n",Data_Uint16_1,Data_Uint16_2);
  printf("轉換後的8位整數：0x%x,0x%x,0x%x,0x%x\n",Data_Uint8_1,Data_Uint8_2,Data_Uint8_3,Data_Uint8_4);

  printf("-------------------經過結構運算-------------------\n");     
  printf("字符A，ASCII爲01000001，結構轉換後的內容\n");  
  memcpy(&Test1, C1, sizeof(Test1));  
  printf("Test1.Byte08=%d \n",Test1.Byte08);  
  printf("Test1.Byte07=%d \n",Test1.Byte07);  
  printf("Test1.Byte06=%d \n",Test1.Byte06);  
  printf("Test1.Byte05=%d \n",Test1.Byte05);  
  printf("Test1.Byte04=%d \n",Test1.Byte04);  
  printf("Test1.Byte03=%d \n",Test1.Byte03);  
  printf("Test1.Byte02=%d \n",Test1.Byte02);  
  printf("Test1.Byte01=%d \n",Test1.Byte01);  

  Data_Uint8_1=0x89;Data_Uint8_2=0xAB;Data_Uint8_3=0xCD;Data_Uint8_4=0xEF;
  printf("-------------------經過位運算合併-------------------\n");
  Data_Uint16_1 = (unsigned short int)(Data_Uint8_1 << 8) | (unsigned short int)(Data_Uint8_2);
  Data_Uint16_2 = (unsigned short int)(Data_Uint8_3 << 8) | (unsigned short int)(Data_Uint8_4);
  Data_Uint32=(unsigned int) (Data_Uint16_1 << 16) | (unsigned int)(Data_Uint16_2);
  printf("合併前的8位整數：0x%x,0x%x,0x%x,0x%x\n",Data_Uint8_1,Data_Uint8_2,Data_Uint8_3,Data_Uint8_4);
  printf("合併後的16位整數：0x%x,0x%x\n",Data_Uint16_1,Data_Uint16_2);
  printf("合併後的32位整數：0x%x\n",Data_Uint32);

return 0;

}
輸出：

在這裏練習之後進入Keil uVision5編程，想寫個通用的轉換函數，後面想沒有必要，難道八、16位、32位相互轉換這麼複雜嗎？若是這樣，寫在Keil uVision5裏面的程序會是多麼複雜，之後本身看起來也會繁瑣的。

接着寫：

直接強制轉換：

printf("-------------------8位到32位轉換-------------------\n");
  Data_Uint8_1=0x00;
  Data_Uint8_2=0x19;
  Data_Uint16_2=0x00;
  Data_Uint16_1 = (unsigned short int)(0x00 << 8) | (unsigned short int)(Data_Uint8_2);
  Data_Uint32=(unsigned int) (0x00 << 16) | (unsigned int)(Data_Uint16_1);
  printf("轉換前的8位整數：0x%x,%d\n",Data_Uint8_2,sizeof(Data_Uint8_2));
  printf("8位到32位轉換1======>轉換後的32位整數：0x%x,數據長度：%d\n",Data_Uint32,sizeof(Data_Uint32));
  Data_Uint32=(unsigned int) (0x00 << 16) | (unsigned int)( (unsigned short int)(0x00 << 8) | (unsigned short int)(Data_Uint8_2));
  printf("8位到32位轉換2======>轉換後的32位整數：0x%x,數據長度：%d\n",Data_Uint32,sizeof(Data_Uint32));
  //Data_Uint32=(unsigned int) (0x00 << 24) | (unsigned int)(Data_Uint8_2);
  Data_Uint32= (unsigned int)(Data_Uint8_2);
  printf("8位到32位轉換3======>轉換後的32位整數：0x%x,數據長度：%d\n",Data_Uint32,sizeof(Data_Uint32));
  Data_Uint32=0x69;
  Data_Uint8_1= (unsigned char)(Data_Uint32);
  printf("32位整數：0x%x,數據長度：%d\n",Data_Uint32,sizeof(Data_Uint32));
  printf("32位到8位轉換======>轉換後的8位整數：0x%x,數據長度：%d\n",Data_Uint8_1,sizeof(Data_Uint8_1));

實際輸出：

-------------------8位到32位轉換-------------------
轉換前的8位整數：0x19,1
8位到32位轉換1======>轉換後的32位整數：0x19,數據長度：4
8位到32位轉換2======>轉換後的32位整數：0x19,數據長度：4
8位到32位轉換3======>轉換後的32位整數：0x19,數據長度：4
32位整數：0x69,數據長度：4
32位到8位轉換======>轉換後的8位整數：0x69,數據長度：1

說明：8位強制轉32位，前面系統自動加了24位的0；32位強制轉8位，系統只截取了最後的8位。