NULL not declared in scope

[Laharl]

I'm writing a class definitionin C++, and I keep getting errors saying "NULL was not declared in previous scope." This happens no matter where in the file NULL is used, except inside a main, it seems. I'm running GCC 4.1.2 on Ubuntu Feisty Fawn (7.04).

An example code snippet is

#include utility //used later in file
using namespace std;
 
template <typename T> 
struct treeNode{
    T data;
    treeNode<T>* left;
    treeNode<T>* right;
    treeNode<T>* parent;
    bool hasBeenIterated;
    treeNode(const T& d = T()) : data(d) {
        hasBeenIterated = false;
        left = NULL;
        right = NULL;
        parent = NULL;
    }
};

Any help you can give me with this bizarre error would be much appreciated!

[ruskalym]

Use 0 instead. Zero is pointer-type compatible in C++, no need to cast it.

[Laharl]

That worked, thanks.