Question

This is my function that is supposed to flip a string such as “Today is a beautiful day”
into “day beautiful a is Today” My nextword function (inside flipstring function) return the index of the beginning of every word in the string and also places ‘\0’ after the word. When I use the function is get the error, segmentation fault (core dumped) and I can’t figure out why.

void flip(char *str)
{
  // reverse the order of the words                                                                
  char buf[256];
  int i[2],k,j=0,c=0;

  //set k to the index of the first word in str 
  k = nextword(str);

  //Create an array (i) of the index of the beginning of every word
  //nextword also places a '\0' after every word in str
  while ( k != -1)
    {

      i[j] = k;
      j++;
      k = nextword(NULL);
    }

  //place each word in buf in reverse order
  //replace the eos with a space  
  for ( j=j-1 ; j >= 0 ; j--)    //starts with index of last word in string str
    {
     buf[c]=str[i[j]];
           while(buf[c]!='\0')
             {
           c++;
           buf[c]=str[i[j]+c];
          }

       buf[c] = ' ';  //replaces '\0' after every word with a space
       c=c+1;
    } 
  buf[c] = '\0';  //Places eos at the end of the string in buf
   printf("%s\n",buf[0]);

}

Call it,

void main(void)
{
  char str[] = "Today is a beautiful day!\t\n";
  flip(str);
  //printf("%s",str);
}

Answer 1

In printf("%s\n",buf[0]); you’re passing a character to printf instead of a string which will cause a segmentation fault. Use printf("%s\n", buf); instead.

Also you aren’t copying the words correctly, in buf[c]=str[i[j]+c]; c is not the offset from the beginning of the current word but from the beginning of buf, you should use another counter to use as the offset.

l = 0;
while(buf[c]!='\0'){
   c++;
   l++;
   buf[c]=str[i[j]+l];
}