Seg Fault in Knowledge Tree

Question

I am implementing a knowledge tree in c that can read from a file. I am getting a seg fault in my newStr function. I\'m not able to test the rest of my code with this problem. I

Answer 1

There might be several more, but here's some points on what's wrong:

1. Your newStr function is just very, very wrong. At a guess you'd want something like:

   char * newStr (char * charBuffer)
   {
     char *newStr;
     if(charBuffer[0] == 'A' || charBuffer[0] == 'Q') {
       newStr = strdup(&charBuffer[1]);
     } else {
       newStr = strdup("");
     }
     if(newStr == NULL) {
         //handle error
     }
     return newStr;
   }
   

2. You can't cast a string to a char like you do here:

    if(ans[0] == (char)"Y" || ans[0] == (char)"y")
   

   Do instead(same for similar code elsewhere too)

    if(ans[0] =='Y' || ans[0] == 'y')
   

3. Same as above when you call putc, don't do

    fputc((char)"A", f);
   

   Do

    fputc('A', f);
   

4. scanf needs a format string, don't do:

   scanf(ans);
   

   Do e.g. (or just use fgets again)

   if(scanf("%99s",ans) != 1) {
      //handle error
    }
   

Answer 2

"+" operator as string concatenation does not work in c.

If you actually want to copy the a string use strdup(). This function allocates memory and copies the string into it.

Don't forget to free the allocated memory when done using it.

Answer 3

char * newStr (char * charBuffer)
{
  int i;
  int length = strlen(charBuffer);
  char newStr;
  if(charBuffer[0] == 'A' || charBuffer[0] == 'Q'){
    for(i=1; i<length; i++)
        newStr += charBuffer[i]; 
  }
  return (newStr + "\0");
}

Well, there's a few interesting things here... To get down to brass tacks, you're trying to copy the contents of a character pointer into another and this function isn't going to do that. All you're really doing is summing the value of each char in charBuffer into newStr because a char is really just an 8-bit integer and then you return that integer as a pointer through an implicit cast so it is now being treated as a memory address.

You should look to use strdup(), as has been noted, since this is exactly what the function is supposed to do. No need to reinvent the wheel. :)