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  1. #include<stdio.h>
  2. #include<string.h>
  3. #include<stdlib.h>
  4.  
  5. struct a
  6. {
  7.     void *ptr;
  8.     unsigned long val;
  9. };
  10.  
  11. void func(struct a *id,void *ptr)
  12. {    
  13.     memset(id, 0, sizeof(*id));
  14.  
  15.     id->ptr = ptr;
  16.     if (sizeof(id->val) >= sizeof(id->ptr))
  17.     {    
  18.         id->val = (unsigned long)id->ptr;
  19.     }
  20.  
  21. }
  22. void func2(struct a *id)
  23. {
  24.     unsigned char errno;
  25.     printf("errno-address=%lu\n", &errno);
  26.     func(id,&errno);
  27. }
  28.  
  29. int main()
  30. {
  31.     struct a *id;
  32.     id = malloc(sizeof(*id));
  33.     func2(id);
  34.     printf("after-changing=%lu\n", id->val);
  35.     return 0;
  36. }
  37.  
  38.  
Success #stdin #stdout 0.01s 1808KB
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stdin
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Standard input is empty
stdout
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errno-address=3219979511
after-changing=3219979511
https://ideone.com/ZH3Ws
language:
C (gcc 8.3)
created:
11 years ago
visibility:
public

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