Question

So I did a bit of C programming a while ago and basically forgot it all lol but anyways I started doing this “C Refresher” thing I found online and was following this binary search tree example kinda loosely and ran into an error. Once I compile it and run it, it says “Error: Can’t Open Display”. I am running this code on some kinda Linux server in school. Anyways, here’s the code:

#include <stdio.h>
#include <stdlib.h>

#define TRUE 1
#define FALSE 0 

typedef struct Node {
  int value;
  struct Node *left;
  struct Node *right;
} Node; 

void add (Node *node, int value)
{
  if (value < node->value) {
    //left side 
    if (node->left == NULL) {
      Node *newNode = malloc(sizeof(Node));
      newNode->value = value;
      newNode->left = NULL;
      newNode->right = NULL; 
      node->left = newNode;
    } else {
  add(node->left, value);
    }
  } else {
    //right side 
    if (node->right == NULL) {
      Node *newNode = malloc(sizeof(Node));
      newNode->value = value;
      newNode->left = NULL;
      newNode->right = NULL;
      node->right = newNode;
    } else {
      add(node->right, value);
    }
  }
}

int search(Node *node, int value)
{
  if (node == NULL) {
    return FALSE;
  } else if (node->value == value) {
    return TRUE;
  } else {
    if (value < node->value) {
      return search(node->left, value);
    } else {
      return search(node->right, value);
    }
  }
}

int main (int argc, char *argv[])
{
  Node root;

  root.value = 23;
  root.left = NULL;
  root.right = NULL; 

  add(&root, 5);
  add(&root, 50);
  add(&root, 8);
  add(&root, 2);
  add(&root, 34); 

  if (search(&root, 23)) {
    printf("23 lives in the tree.\n");
  } else {
    printf("23 does not live in the tree.\n");
  }

  if (search(&root, 42)) {
    printf("42 lives in the tree.\n");
  } else {
    printf("42 does not live in the tree.\n");
  }

  return 0;
}

The code might seem long but it is actually pretty basic. I think I coulda cut some of the code out before pasting it here but I figured I would leave everything in in case I took out something vital to the problem.

Also I thought it might have something to do with the Node thing so in my main method I put a quick printf("hi"); before the Node root; to see if that would make a difference but it still gave me the same error. And I have another program on my account on this school server and that program has some printf statements and it runs just fine.

I tried Googling the problem but all this weird Linux threads came up and I couldn’t really understand it. My computer is Windows but I did all this coding in a program called emacs that I got to through a program called PuTTY that lets me connect to the school Linux server.

Also I compiled it with gcc -o tree tree.c.

Sorry for all the writing, I was just trying to give as much information as possible. Thanks to anyone who can help!

Answer 1

Are you invoking it like “./tree” or just “tree”. It looks like you are trying to run a gui application over ssh. To see which application try connecting with “ssh -XY HOST” if you are on a linux machine. Then you should see an application launching.