Same output when printing out a tree in C-CodePudding

struct Node{
  char *key;
  struct Node *sx, *dx;
};

typedef struct Node Node;

int main(void){
  Node *root = NULL;

  char *str = malloc(sizeof(char)*5);

  if(scanf("%s", str) == 1) root = insert(root, str);

  while(strcmp(str, "#end") != 0){
    if(scanf("%s", str) == 1)
      if(strcmp(str, "#end") != 0) insert(root, str);
      else break;
    else printf("error\n");
  }

  printTree(root);
}

I have a BST with the key as a string, and I want to insert multiple strings in the tree, but when I print the tree with the printTree function, print only "#end" many times as the number of strings I inserted.

Here it is an example Output:

$ ./out
hi
all
how 
are
you
#end
#end
#end
#end
#end
#end

The values I type go into the tree (checked with a search algorithm), so I expect the differents value when the tree is printed.

Does anyone knows how to solve it?

CodePudding user response：

You have to allocate a buffer for each strings instead of allocating only one buffer and reusing (overwriting with new strings) that.

  while(strcmp(str, "#end") != 0){
    str = malloc(sizeof(char)*5); // add this here to allocate new buffer for new string
    if(scanf("%4s", str) == 1)
      if(strcmp(str, "#end") != 0) insert(root, str);
      else break;
    else printf("error\n");
  }

Also you should use %4s (in this case) instead of %s for scanf() to limit the number of characters to read and avoid buffer overrun.

CodePudding user response：

As MikeCAT explained, each new node needs to preserve its own discrete key.

main() can be greatly simplified. Here the max key length must be < 128.

void main( void ) {
    Node *root = NULL;

    for( ;; ) {
        char str[128];

        if( scanf( "%s", str ) == 1 ) {
            if( strcmp( str, "#end" ) == 0 )
                break;
            root = insert( root, str );
        }
    }
    printTree(root);
}

and strdup() can be used to preserve the key for the new node.

Node* newNode( char *key ) {
    Node *tmp = (Node*)malloc( sizeof(Node) );
    tmp->key = strdup( key );
    tmp->sx = tmp->dx = NULL;
    return tmp;
}