【急】数值转换小程序

ahui886

1. #include <stdio.h>
   
2. #include <stdint.h>
   
3. 
   
4. typedef union
   
5. {
   
6.   uint8_t byte[2];
   
7.   uint16_t word;
   
8. } xxx_t;
   
9. 
   
10. int main( void )
    
11. {
    
12.   xxx_t test =
    
13.   {
    
14.     .byte[1] = 0x8b,
    
15.     .byte[0] = 0xd7
    
16.   };
    
17. 
    
18.   uint16_t b;
    
19. 
    
20.   b = test.word;
    
21. 
    
22.   printf( "b = %hu\n", b );
    
23. 
    
24.   return 0;
    
25. }

复制代码

紫柳

定义字节序宏，不同字节序采用不同的组合方法

zsszss0000

这种写法会出问题

1. #include <iostream>
   
2. #include <stdio.h>
   
3. #include <string.h>
   
4. using namespace std;
   
5. int main ( int argc, char *argv[] )
   
6. {
   
7.         char s_c[2]={0};
   
8.         unsigned char u_c[2]={0};
   
9.        
   
10.         int s_i=0;
    
11.         unsigned int u_i=0;
    
12.         signed short int s_s=0;
    
13.         unsigned short int u_s=0;
    
14. 
    
15.         s_c[0]=0x2E;
    
16.         s_c[1]=0xE0;
    
17. 
    
18.         u_c[0]=0x2E;
    
19.         u_c[1]=0xE0;
    
20. 
    
21.         printf ( "%x %x %x %x\n",s_c[0],s_c[1],u_c[0],u_c[1]);
    
22.         printf ( "%x %x %x %x\n",s_c[0]<<8,s_c[1],u_c[0]<<8,u_c[1]);
    
23.         printf ( "%x %x\n",s_c[0]<<8+s_c[1],u_c[0]<<8+u_c[1]);
    
24.         printf ( "%x %x\n",s_c[0]<<8|s_c[1],u_c[0]<<8|u_c[1]);
    
25.         printf ( "%x %x\n",s_c[0]*256+s_c[1],u_c[0]*256+u_c[1]);
    
26.         printf ( "%x %x\n",s_c[0]*0x100+s_c[1],u_c[0]*0x100+u_c[1]);
    
27. 
    
28.         cout<<endl<<endl;
    
29. 
    
30.         cout<<"aaaaaaaaaa"<<endl;
    
31.         s_i=u_c[0]<<8+u_c[1];
    
32.         u_i=u_c[0]<<8+u_c[1];
    
33.         s_s=u_c[0]<<8+u_c[1];
    
34.         u_s=u_c[0]<<8+u_c[1];
    
35. 
    
36.         cout<<dec<<s_i<<":"<<hex<<"0x"<<s_i<<endl;
    
37.         cout<<dec<<u_i<<":"<<hex<<"0x"<<u_i<<endl;
    
38.         cout<<dec<<s_s<<":"<<hex<<"0x"<<s_s<<endl;
    
39.         cout<<dec<<u_s<<":"<<hex<<"0x"<<u_s<<endl;
    
40. 
    
41.         cout<<"bbbbbbbbbb"<<endl;
    
42.         s_i=u_c[0]<<8|u_c[1];
    
43.         u_i=u_c[0]<<8|u_c[1];
    
44.         s_s=u_c[0]<<8|u_c[1];
    
45.         u_s=u_c[0]<<8|u_c[1];
    
46. 
    
47.         cout<<dec<<s_i<<":"<<hex<<"0x"<<s_i<<endl;
    
48.         cout<<dec<<u_i<<":"<<hex<<"0x"<<u_i<<endl;
    
49.         cout<<dec<<s_s<<":"<<hex<<"0x"<<s_s<<endl;
    
50.         cout<<dec<<u_s<<":"<<hex<<"0x"<<u_s<<endl;
    
51. 
    
52.         cout<<"cccccccccc"<<endl;
    
53.         s_i=u_c[0]*0x100+u_c[1];
    
54.         u_i=u_c[0]*0x100+u_c[1];
    
55.         s_s=u_c[0]*0x100+u_c[1];
    
56.         u_s=u_c[0]*0x100+u_c[1];
    
57. 
    
58.         cout<<dec<<s_i<<":"<<hex<<"0x"<<s_i<<endl;
    
59.         cout<<dec<<u_i<<":"<<hex<<"0x"<<u_i<<endl;
    
60.         cout<<dec<<s_s<<":"<<hex<<"0x"<<s_s<<endl;
    
61.         cout<<dec<<u_s<<":"<<hex<<"0x"<<u_s<<endl;
    
62. 
    
63.         return 1;
    
64. }
    

复制代码

2e ffffffe0 2e e0
2e00 ffffffe0 2e00 e0
2e00 2e00
ffffffe0 2ee0
2de0 2ee0
2de0 2ee0


aaaaaaaaaa
11776:0x2e00
11776:0x2e00
11776:0x2e00
11776:0x2e00
bbbbbbbbbb
12000:0x2ee0
12000:0x2ee0
12000:0x2ee0
12000:0x2ee0
cccccccccc
12000:0x2ee0
12000:0x2ee0
12000:0x2ee0
12000:0x2ee0


红颜色标记的部分不对吧，为什么不等于0x2ee0呢？
u_c[0]<<8+u_c[1];
和
=u_c[0]<<8|u_c[1];
到底有什么差别呢？


回复 4# hellioncu


   

hellioncu

zsszss0000 发表于 2015-04-10 14:13
这种写法会出问题2e ffffffe0 2e e0
2e00 ffffffe0 2e00 e0
2e00 2e00

优先级问题，请加上括号

zsszss0000

好了，大神！
优先级这种问题真的很头疼！！！回复 14# hellioncu


   

hellioncu

zsszss0000 发表于 2015-04-10 14:41
好了，大神！
优先级这种问题真的很头疼！！！回复 14# hellioncu

自己拿不准的就加上括号吧，人家看了也明白。
现在有些编译器比较智能，会给你警告的，留意下就行

花依然绽放