help required with memcpy

[foniks munkee]

Hi - Been trying to make sense of memcpy and void pointers. I have a project that I am trying to complete which requires that I use memcpy to copy data of any type from a user of the program to a variable of type void. However I have not been able to get it to work with scalar variables of type int. But it does work with any other type of data including complex data structures. Any ideas?

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

int main(void)
{
	int *pInt;
	void *pVoid;

	pInt = (int *) malloc(sizeof(int));
	if(pInt == NULL)
	{
		printf("Error Allocating memory!");
		exit(1);
	}

	pVoid = (void *) malloc(sizeof(int));
	if(pVoid == NULL)
	{
		printf("Error Allocating memory!");
		exit(1);
	}

	printf("Enter a number: ");
	scanf("%d", &pInt);
	
	memcpy(pVoid, pInt, sizeof(int));

	return 0;
}

[hk_mp5kpdw]

scanf("%d", &pInt);

Since your pInt variable is already a pointer, and scanf takes a pointer argument, you should not be using the "address of" operator here. Take it out. Try this:

scanf( "%d", pInt );

See if that solves your problem. I only took a quick glance at the code and nothing else popped out at me as being an issue except maybe use a void pointer type cast for the second arugment of the memcpy perhaps.

[foniks munkee]

Since your pInt variable is already a pointer, and scanf takes a pointer argument, you should not be using the "address of" operator here. Take it out. Try this:

Yup Your right it works.. Thanks! This wasn't a good example of the problem I am having then. D'oh. The following code is probably pretty familiar to a few by now..
I call the following function in this manner:

insert(pMylist, pData, sizeof(pData));

Now, if pData is a pointer of type struct it works. If it is a pointer of type int, it does not work. This function has to be generic!!! But from what I can tell calling memcpy like this:

// ..works in the following function if pData is struct * data type
memcpy(pNewnode->data, pData, size);
// ..works in the following function if pData is int * data type
memcpy(&pNewnode->data, pData, size);

int insert(DLL *pRoot, void *pData, size_t size)
{
	NODE *pNewnode;

	// Allocate memory for the next node in the list
	if ((pNewnode = (NODE *) malloc(sizeof(NODE))) == NULL)
	{
		printf("Error: Unable to allocate memory for pNewnode");
		fflush(stdout);
		exit(EXIT_FAILURE);
	}

	// Allocate memory for the input from user
	if ((pNewnode->data = malloc(size)) == NULL)
	{
		printf("Error: Unable to allocate memory for pNewnode->data");
		fflush(stdout);
		exit(EXIT_FAILURE);
	}
	
	pNewnode->next = NULL;
	pNewnode->prior = NULL;

	// Copy the data to the new node: This bit currently broken
	memcpy(pNewnode->data, pData, size);
	
	if (pRoot->head == NULL)
	{
		pRoot->head = pNewnode;
		pRoot->tail = pNewnode;
		pRoot->count = 1;
	}
	else
	{
		pNewnode->prior = pRoot->tail;
		pRoot->tail->next = pNewnode;
		pRoot->tail	= pNewnode;
		pRoot->count += 1;				// Increase the count for the number of nodes
	}
	
	return 1;
}