C语言条件编译

 1 #include <stdio.h> 
 2  
 3 void main() 
 4 { 
 5 #ifdef AAA 
 6     printf("find AAA defined\n"); 
 7 #else 
 8     printf("find nothing\n"); 
 9 #endif 
10 } 
11  
12 void main() 
13 { 
14 #if AAA 
15     printf("find AAA defined\n"); 
16 #else 
17     printf("find nothing\n"); 
18 #endif 
19 } 
20  
21 gcc aa.c -o pp -D AAA 
22  
23 两个程序都打印：find AAA defined