free() question

This is a discussion on free() question within the C Programming forums, part of the General Programming Boards category; Hi all: I declared a structure in the .h file to implement a stack: typedef struct VIEW_MEMBER_TAG { char *ptrString; ...

  1. #1
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    Question free() question

    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:

    Code:
      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

  2. #2
    C++ Witch laserlight's Avatar
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    How are you creating the stack? Is ptrString dynamically allocated, or at least initialised to NULL?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
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    Code:
    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;
    }

  4. #4
    and the Hat of Guessing tabstop's Avatar
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    Code:
    stackPtr->ptrNextViewMember = stackPtr;
    Other way around, perhaps? I don't see how stackPtr ever changes in your loop.

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