free() question

[yuzhangoscar]

Hi all:

I declared a structure in the .h file to implement a stack:

typedef struct VIEW_MEMBER_TAG
{
char *ptrString;
struct VIEW_MEMBER_TAG *ptrNextViewMember;
}VIEW_MEMBER;

In .c file:

static VIEW_MEMBER* stackPtr; //It is the pointer that points to the top of the stack.


Later I need to free up the stack so I wrote:

  void freeStack(void)
{
	while (stackPtr != NULL)
	{
		free(stackPtr->ptrString);  //This line holds up the program.
		stackPtr->ptrString = NULL;
		stackPtr->ptrNextViewMember = stackPtr;
	}
}

This line holds up the whole program.

free(stackPtr->ptrString);


Can anyone help me out?

Cheers

[laserlight]

How are you creating the stack? Is ptrString dynamically allocated, or at least initialised to NULL?

[yuzhangoscar]

void push(char* string)
{
	size_t N = 0;
	VIEW_MEMBER* newmem = NULL;

	newmem = (VIEW_MEMBER*)malloc(sizeof(VIEW_MEMBER));    //Need to check for error here.

	InitializeStack(newmem); 

	N = strlen(string)+1;
	newmem->ptrString = (char*)malloc(N);     //Need to check for error here.
	strncpy(newmem->ptrString, string, N);
	newmem->ptrString[N] = '\0';

	if (stackPtr == NULL)
	{
		stackPtr = newmem;
	}
	else
	{
		newmem->ptrNextViewMember = stackPtr;
		stackPtr = newmem;
	}
}

void InitializeStack(VIEW_MEMBER *newMember)
{
	newMember->ptrString = NULL;
	newMember->ptrNextViewMember = NULL;
}

[tabstop]

stackPtr->ptrNextViewMember = stackPtr;

Other way around, perhaps? I don't see how stackPtr ever changes in your loop.