Question

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Why does simple C code receive segmentation fault?

I have code below which will remove trailing spaces from a string but i don’t what
going in this code so as it gives segmentation fault problem??

 void main(void);

char* rtrim(char*);

void main(void)
 { 
 char* trail_str = "This string has trailing spaces in it.               ";


 printf("Before calling rtrim(), trail_str is '%s'\n", trail_str);

 printf("and has a length of %d.\n", strlen(trail_str));



 rtrim(trail_str);



 printf("After calling rtrim(), trail_str is '%s'\n", trail_str);

 printf("and has a length of %d.\n", strlen(trail_str));

 }


  char* rtrim(char* str)
  {
   int n = strlen(str) - 1;    

    while (n>0)            
   {
       if (*(str+n) != ' ')    
      {

           *(str+n+1) = '\0'; 



           break;             
      }

      else

      n--;
 }

 return str;      

 }

Answer 1

trail_str points to a constant area in the memory and thus cannot be changed in *(str+n+1) = '\0'

when initializing

char* trail_str = "This string has trailing spaces in it.               ";

you actualy generate a constant string: "This string has trailing spaces in it. " and tell trail_str to point to it.