#22. gcc的GNU扩展

标签(label)引用 :

片段1 :

  1 #include <stdio.h>
  2
  3
  4 int main( int argc , char **argv )
  5 {
  6
  7
  8 if(1){
  9                 printf("point A\n" );
 10                 goto error;
 11         }
 12
 13         if(1){
 14                 printf("point B\n");
 15         }
 16
 17 error :
 18
 19         printf("point C\n");
 20
 21
 22         return 0;
 23 }

    xuk@localhost:~/svn/goodbyeworld/binary-hacks/22/lable$ gcc main.c
    xuk@localhost:~/svn/goodbyeworld/binary-hacks/22/lable$./a.out

     

    point A
    point C

  片段 2 :
 

1 #include <stdio.h>
  2
  3 int main( int argc , char **argv )
  4 {
  5         void *lable;
  6         lable = &&error;
  7
  8         if(1){
  9                 printf("point A\n" );
 10                 goto *lable;
 11         }
 12
 13         if(1){
 14                 printf("point B\n");
 15         }
 16
 17 error :
 18         printf("point C\n");
 19
 20         return 0;
 21 }

06:10:41-xuk@localhost:~/svn/goodbyeworld/binary-hacks/22/lable$gcc main.c
06:10:42-xuk@localhost:~/svn/goodbyeworld/binary-hacks/22/lable$./a.out
point A
point C

片段 3 :

#include <stdio.h>
  2
  3 int main( int argc , char **argv )
  4 {
  5         static int labels[] = { &&label0 - &&label0 , &&label1 - &&label0 , &&label2 -&&label0 };
  6         int i = 0;
  7
  8         goto *(&&label0 + labels[i]);
  9
 10         label0 :
 11                 printf("point A\n" );
 12         label1 :
 13                 printf("point B\n" );
 14         label2 :
 15                 printf("point C\n" );
 16
 17         return 0;
 18 }

根据 i 的取值不同 , 会跳到不同的label$