Thread: Accessing a quad tree data structure

The lecturer has written several functions to handle a quad tree data structure, all we have to do is access it to print an ASCII image.

The function for uploading the image works fine, but when I try to access the print function, it gives me a seg fault. In dark red is the function call I made.

I guess I did it wrong? Also there is a lot more code, but I just included the bits that concerned this part of the program.

Code:

typedef struct qtnode QTnode;

struct qtnode {
    char   type;// ' ','*' or INTERNAL
    QTnode *ne; // north east quadrant
    QTnode *nw; // north west quadrant
    QTnode *sw; // south west quadrant
    QTnode *se; // south east quadrant
    QTnode *out;// zoomed-out image
};


void printImage(QTnode *qt, int dim)
{
  char *buffer;
  int i;

  // reserve memory for file contents
  if((buffer = (char *) malloc(dim * dim)) == NULL) {
    printf("Error - out of memory.\n");
    exit(1);
  }
  // intialise buffer
  for( i = 0; i < dim * dim; buffer[i++] = ' ' )
    ;
  // decode quad tree into image buffer
  createBuffer(qt, buffer, 0, 0, dim, dim);
  printBuffer(buffer, dim); // print buffer
  free(buffer);
}






QTnode *flag;
printImage(flag->type, dimen);

Well, with your call, you don't initialize flag.

This translates, in printImage(), into qt not being initialized.

The only place in printImage() where qt is used is here:

Code:

createBuffer(qt, buffer, 0, 0, dim, dim);

So unless that function sets qt to something (or ignores qt entirely), in other words if it assumes that qt has a value, it is going to crash.

I'm guessing it takes information from qt and puts it into buffer, because of this comment.

Code:

// decode quad tree into image buffer

In other words, you need to get information into the QTnode *flag somehow. You haven't provided enough information for me to tell how.

That's assuming, of course, that this is your real code.

Code:

QTnode *flag;
printImage(flag, dimen);

Casting malloc() is also probably not a good idea, see the FAQ.

[edit] And EOF can't fit into a char, it needs an int. Also see the FAQ. [/edit]

Right, exactly. There's probably a function that reads a QTnode from a file or something. See if you can find it.

Or post the prototypes of all of the functions you have access to.