my linked list code - comments please

Would some of you experienced programmers please comment on my double linked lists code? Many thanks!

(Special thanks to Dave_Sinkula for getting me past a mental block!)

I am expecially concerned about possible "gotcha's", things I have not taken into consideration.

Code:

#include <stdio.h>

typedef struct node NODE;
struct node {
    NODE *pNext;
    NODE *pPrev;
    char *pLine;
};
NODE *head;
NODE *tail;

int initList();  // init with NULL head/tail
void insertAtBeginning(NODE *);
void insertAtEnd(NODE *);
void insertBefore(NODE *, NODE *);
void insertAfter(NODE *, NODE *);
void removeNode(NODE *);

void traverseForward(NODE *);
void traverseBackward(NODE *);

void doSomething(NODE *pNode);
NODE * getNode();

int main(int argc, char *argv[]) {
    char buf1[] = "this is buf 1.";
    char buf2[] = "this is buf 2.";
    char buf3[] = "this is buf 3.";
    NODE *ppp;

    if ( initList() == 0 )
        printf("initList malloc failed.\n");

    ppp = getNode();  // for simplicity here, error checking is done in getNode()
    ppp->pLine = buf1;
    insertAtEnd(ppp);          // 1

    ppp = getNode();
    ppp->pLine = buf2;
    insertAtBeginning(ppp);    // 2 1

    NODE *ppp2 = getNode();
    ppp2->pLine = buf3;
    insertAfter(ppp, ppp2);   // 2 3 1

    traverseForward(head);    // print list
    traverseBackward(tail);

    removeNode(ppp2);         // 2 1
    free(ppp2);

    traverseForward(head);
}


int initList() {

    head = (NODE *) malloc(sizeof(NODE));
    if (head == NULL)
        return 0;

    tail = (NODE *) malloc(sizeof(NODE));
    if (tail == NULL)
        return 0;

    head->pNext = tail;
    head->pPrev = NULL;
    head->pLine = NULL;

    tail->pNext = NULL;
    tail->pPrev = head;
    tail->pLine = NULL;

    return 1;
}

void insertAtBeginning(NODE *pNewNode) {
    insertAfter(head, pNewNode);
}

void insertAtEnd(NODE *pNewNode) {
    insertBefore(tail, pNewNode);
}

void insertBefore(NODE *pNode, NODE *pNewNode) {
    pNewNode->pPrev = pNode->pPrev;
    pNewNode->pNext = pNode;
    pNode->pPrev->pNext = pNewNode;
    pNode->pPrev = pNewNode;
}

void insertAfter(NODE *pNode, NODE *pNewNode) {
    pNewNode->pPrev = pNode;
    pNewNode->pNext = pNode->pNext;
    pNode->pNext->pPrev = pNewNode;
    pNode->pNext = pNewNode;
}

void removeNode(NODE *pNode) {
    pNode->pPrev->pNext = pNode->pNext;
    pNode->pNext->pPrev = pNode->pPrev;

    //free(pNode);  // should be done by caller, if finished with this node
}

void traverseForward(NODE *pNode) {
    NODE *ppp = pNode;
    if (ppp == head)
        ppp = head->pNext;
    while (ppp != tail) {
        doSomething(ppp);   // do whatever... with this node
        ppp = ppp->pNext;
    }
}

void traverseBackward(NODE *pNode) {
    NODE *ppp = pNode;
    if (ppp == tail)
        ppp = tail->pPrev;
    while (ppp != head) {
        doSomething(ppp);   // do whatever... with this node
        ppp = ppp->pPrev;
    }
}

void doSomething(NODE *pNode) {
    printf("%s\n",pNode->pLine);
}

NODE *getNode() {
    NODE *ppp;
    ppp = (NODE *) malloc(sizeof(NODE));
    if ( ppp == NULL ) {
        printf("malloc failed.\n");
        exit(0);
    }
    return ppp;
}

hi,

I wanne to know as to what you want us to do ? send you review comments on ur code on the way its writen.. or try to find bug in ur code .. ??

Since you call malloc, free, and exit, you should add this.

Code:

#include <stdlib.h>

Here you are either using C99 or C++. Declarations may not follow statements in older C.

Code:

    NODE *ppp2 = getNode();

Similarly, these are not necessarily prototypes for functions taking no arguments in C.

Code:

int initList();  // init with NULL head/tail
NODE * getNode();

http://david.tribble.com/text/cdiffs.htm#C99-empty-parm

The following cast is not necessary in C.

Code:

ppp = (NODE *) malloc(sizeof(NODE));

FAQ > Explanations of... > Casting malloc

Thank you Dave! Really good stuff!

I:
- bookmarked those 2 links you gave. (I'm still absorbing them)
- took off the cast to malloc.
- put in the "#include <stdlib.h>" (I had wondered about that)
- fixed my prototypes for my 2 functions with no arguments
- put my ppp2 declaration before all statements (not C99)

ok, I'm off to my next task.