C语言编程中的8位、16位、32位整数的分解与合并

　　在单片机的编程中对于8位、16位、32位整数的分解与合并用的比较多，今天做了简要学习，后面还需要加以总结。

　　练习在VC++6.0编程环境中进行，源程序：

1. #include <stdio.h>
2. #include 'string.h'
4. int main(int argc, char* argv[])
5. {
6. unsigned int Data_Uint32=0x12345678;
7. unsigned short int Data_Uint16_1,Data_Uint16_2;
8. unsigned char Data_Uint8_1,Data_Uint8_2,Data_Uint8_3,Data_Uint8_4;
9. struct StructByte8{
10. unsigned char Byte01:1;
11. unsigned char Byte02:1;
12. unsigned char Byte03:1;
13. unsigned char Byte04:1;
14. unsigned char Byte05:1;
15. unsigned char Byte06:1;
16. unsigned char Byte07:1;
17. unsigned char Byte08:1;
18. } Test1;
19. unsigned char C1[]='A';
20. //定义16位的指针将32位地址强制转为16位，高位丢弃取低位
21. unsigned short int *p16=(unsigned short int *)(&Data_Uint32);
22. unsigned short int Data_Uint16_2p,Data_Uint16_1p;
24. printf('32位整数：0x%x\n',Data_Uint32);
25. printf('-------------------通过指针运算-------------------\n');
26. Data_Uint16_2p=*(unsigned short int *)p16;
27. Data_Uint16_1p=*((unsigned short int *)p16+1);
28. printf('转换后的16位整数：0x%x,0x%x\n',Data_Uint16_1p,Data_Uint16_2p);
30. Data_Uint8_1= *(unsigned char *)p16;
31. Data_Uint8_2= *((unsigned char *)p16+1);
32. Data_Uint8_3= *((unsigned char *)p16+2);
33. Data_Uint8_4= *((unsigned char *)p16+3);
34. printf('转换后的8位整数：0x%x,0x%x,0x%x,0x%x\n',Data_Uint8_1,Data_Uint8_2,
35. Data_Uint8_3,Data_Uint8_4);
36. Data_Uint8_1=0;Data_Uint8_2=0;Data_Uint8_3=0;Data_Uint8_4=0;
37. //直接根据指针取值
38. //将32位的整数分解成两个16位的整数,再取低位的16位
39. //强制转换，丢弃高位的16位
40. //32位转16位
41. Data_Uint16_1=(unsigned short int)(Data_Uint32>>16);
42. Data_Uint16_2=(unsigned short int)Data_Uint32;
44. //32位转8位
45. Data_Uint8_1= (unsigned char)(Data_Uint32>>24);
46. Data_Uint8_2= (unsigned char)(Data_Uint32>>16);
47. Data_Uint8_3= (unsigned char)(Data_Uint32>>8);
48. Data_Uint8_4= (unsigned char)Data_Uint32;
50. printf('-------------------通过位运算-------------------\n');
51. printf('转换后的16位整数：0x%x,0x%x\n',Data_Uint16_1,Data_Uint16_2);
52. printf('转换后的8位整数：0x%x,0x%x,0x%x,0x%x\n',Data_Uint8_1,Data_Uint8_2,
53. Data_Uint8_3,Data_Uint8_4);
55. printf('-------------------通过结构运算-------------------\n');
56. printf('字符A，ASCII为01000001，结构转换后的内容\n');
57. memcpy(&Test1, C1, sizeof(Test1));
58. printf('Test1.Byte08=%d \n',Test1.Byte08);
59. printf('Test1.Byte07=%d \n',Test1.Byte07);
60. printf('Test1.Byte06=%d \n',Test1.Byte06);
61. printf('Test1.Byte05=%d \n',Test1.Byte05);
62. printf('Test1.Byte04=%d \n',Test1.Byte04);
63. printf('Test1.Byte03=%d \n',Test1.Byte03);
64. printf('Test1.Byte02=%d \n',Test1.Byte02);
65. printf('Test1.Byte01=%d \n',Test1.Byte01);
67. Data_Uint8_1=0x89;Data_Uint8_2=0xAB;Data_Uint8_3=0xCD;Data_Uint8_4=0xEF;
68. printf('-------------------通过位运算合并-------------------\n');
69. Data_Uint16_1 = (unsigned short int)(Data_Uint8_1 << 8) | (unsigned short int)(Data_Uint8_2);
70. Data_Uint16_2 = (unsigned short int)(Data_Uint8_3 << 8) | (unsigned short int)(Data_Uint8_4);
71. Data_Uint32=(unsigned int) (Data_Uint16_1 << 16) | (unsigned int)(Data_Uint16_2);
72. printf('合并前的8位整数：0x%x,0x%x,0x%x,0x%x\n',Data_Uint8_1,Data_Uint8_2,Data_Uint8_3,Data_Uint8_4);
73. printf('合并后的16位整数：0x%x,0x%x\n',Data_Uint16_1,Data_Uint16_2);
74. printf('合并后的32位整数：0x%x\n',Data_Uint32);
76. return 0;
77. }

输出：

在这里练习以后进入Keil uVision5编程，想写个通用的转换函数，后面想没有必要，难道8、16位、32位相互转换这么复杂吗？如果这样，写在Keil uVision5里面的程序会是多么复杂，以后自己看起来也会繁琐的。

接着写：

直接强制转换：

  printf('-------------------8位到32位转换-------------------\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('转换前的8位整数：0x%x,%d\n',Data_Uint8_2,sizeof(Data_Uint8_2));
  printf('8位到32位转换1======>转换后的32位整数：0x%x,数据长度：%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位转换2======>转换后的32位整数：0x%x,数据长度：%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位转换3======>转换后的32位整数：0x%x,数据长度：%d\n',Data_Uint32,sizeof(Data_Uint32));
      Data_Uint32=0x69;
      Data_Uint8_1= (unsigned char)(Data_Uint32);
  printf('32位整数：0x%x,数据长度：%d\n',Data_Uint32,sizeof(Data_Uint32));
  printf('32位到8位转换======>转换后的8位整数：0x%x,数据长度：%d\n',Data_Uint8_1,sizeof(Data_Uint8_1));

实际输出：

-------------------8位到32位转换-------------------
转换前的8位整数：0x19,1
8位到32位转换1======>转换后的32位整数：0x19,数据长度：4
8位到32位转换2======>转换后的32位整数：0x19,数据长度：4
8位到32位转换3======>转换后的32位整数：0x19,数据长度：4
32位整数：0x69,数据长度：4
32位到8位转换======>转换后的8位整数：0x69,数据长度：1

说明：8位强制转32位，前面系统自动加了24位的0；32位强制转8位，系统只截取了最后的8位。