Pointer to a template function

[Chris Schadl]

Hi,

I'm working on writing a templated Binary Search Tree class in C++. In
regular C, I would have functions which traverse the tree take a pointer
to a user-defined function as an argument, which would then execute the
user-defined function for each node that is "visited". For example:

/* in the BST header file */
/* I actually don't remember if this is valid C or not */
typedef void (*fn)(void* tree_item);
void BST_inorder_traverse(const BST *tree, fn func);
/*...*/
void display_item(void* tree_item);
/*...*/
BST_inorder_traverse(tree, display); /* or something */

However, I'm not entierly certian how to do this in C++ if the BST is a
templated class. Is it possible to use typedef in conjunction with
templates? or is there some other 'correct' way of doing something like
this in C++?

Thanks,

Chris Schadl

[Buster]

Chris Schadl wrote:

I'm working on writing a templated Binary Search Tree class in C++. In
regular C, I would have functions which traverse the tree take a pointer
to a user-defined function as an argument, which would then execute the
user-defined function for each node that is "visited". For example:

/* in the BST header file */
/* I actually don't remember if this is valid C or not */
typedef void (*fn)(void* tree_item);
void BST_inorder_traverse(const BST *tree, fn func);
/*...*/
void display_item(void* tree_item);
/*...*/
BST_inorder_traverse(tree, display); /* or something */

However, I'm not entierly certian how to do this in C++ if the BST is a
templated class. Is it possible to use typedef in conjunction with
templates? or is there some other 'correct' way of doing something like
this in C++?

The standard library uses function objects. See for example the sort
template. You use templates to avoid specifying the type of a function
object. Here's a simple example.

#include <ostream>
#include <iostream>

template <typename Function>
void example (Function func)
{
for (int i = 0; i != 10; ++ i) func (i);
}

void f (int i)
{
std::cout << "Print " << i << " through pointer-to-function.\n";
}

struct g
{
void operator () (int i)
{
std::cout << "Print " << i << " through function object.\n";
}
};

int main ()
{
example (& f);
example (g ());
}

--
Regards,
Buster.

[John Harrison]

"Chris Schadl" <cs*****@satan.blah.org.uk> wrote in message
news:pa****************************@satan.blah.org .uk...

Hi,

I'm working on writing a templated Binary Search Tree class in C++. In
regular C, I would have functions which traverse the tree take a pointer
to a user-defined function as an argument, which would then execute the
user-defined function for each node that is "visited". For example:

/* in the BST header file */
/* I actually don't remember if this is valid C or not */
typedef void (*fn)(void* tree_item);
void BST_inorder_traverse(const BST *tree, fn func);
/*...*/
void display_item(void* tree_item);
/*...*/
BST_inorder_traverse(tree, display); /* or something */

However, I'm not entierly certian how to do this in C++ if the BST is a
templated class. Is it possible to use typedef in conjunction with
templates?

Of course, assuming something like this, where NODE is the type of the node
data (and so the type of the parameter to your function pointer).

template <class NODE>
class BST
{
public:
typedef void (*node_visitor_func)(NODE*);
void inorder_traverse(node_visitor_func func);
};

john