Hi there

I just downloaded Digital Mars & am having problems testing it on a small C program using DOS.  Other small programs seem to work but this one doesn't.  The only difference is that this program uses the malloc() function.

I am getting an access violation:

******************************************************
Application exception occurred:
App:  (pid=468)
When: 28/03/2002 @ 16:19:37.957
Exception number: c0000005 (access violation)
******************************************************

Can you please tell me why this might be happening?

Here is my program:

***********************************************************************
/*  A program that initializes a Linked Deque & presents the user
with a menu to manipulate the Linked Deque.
Functions are included to: Push, Append, Pop, Eject, Print,
Size, Show menu/Clear screen & Quit */

#include <stdio.h>
#include <stdlib.h>
#include <alloc.h>
#include <conio.h>
#include <disp.h>


struct NodeRec
{
int entry;
struct NodeRec* next;
};

typedef struct NodeRec Node;

struct LinkedDequeRec
{
int count;
Node* front;
Node* rear;
};

typedef struct LinkedDequeRec Deque;

/* Make a new node which contains a value */

Node* makeNode (int value)
{
Node* newNodePtr = (Node*)malloc(sizeof(Node));

if (newNodePtr == NULL)
{
fprintf(stderr, "Out of memory");
exit(1);
}

else
{
newNodePtr -> entry = value;
newNodePtr -> next = NULL;
}

return newNodePtr;
}

/* Initialize a Linked Deque to be empty */

void initializeDeque (Deque* dequePtr)
{
dequePtr -> front = NULL;
dequePtr -> rear = NULL;
dequePtr -> count = 0;
}

/* Push an item at the front of a Linked Deque */

void push (Deque* dequePtr, int item)
{
Node* newNodePtr = makeNode(item);

if (newNodePtr != NULL)
{
if (dequePtr -> count == 0)
{
dequePtr -> front = newNodePtr;
dequePtr -> rear = newNodePtr;
dequePtr -> count = 1;
}

else
{
newNodePtr -> next = dequePtr -> front;
dequePtr -> front = newNodePtr;
dequePtr -> count++;
}
}
}

/* Append an item at the rear of a Linked Deque */

void append (Deque* dequePtr, int item)
{
Node* newNodePtr = makeNode(item);

if (newNodePtr != NULL)
{
if (dequePtr -> count == 0)
{
dequePtr -> front = newNodePtr;
dequePtr -> rear = newNodePtr;
dequePtr -> count = 1;
}

else
{
dequePtr -> rear -> next = newNodePtr;
dequePtr -> rear = newNodePtr;
dequePtr -> count++;
}
}
}

/* Pops an item off the front of the Deque & returns it */

int pop (Deque* dequePtr)
{
int item;
Node* oldNodePtr = dequePtr -> front;

if (dequePtr -> count == 0)
{
fprintf(stderr, "Deque is empty!\n");
exit(1);
}

else
{
item = oldNodePtr -> entry;
dequePtr -> front = oldNodePtr -> next;
free(oldNodePtr);
dequePtr -> count--;
}

return item;
}

/* Ejects an item from the rear of the Deque & returns it */

int eject (Deque* dequePtr)
{
int item, rearCount;
Node* newRearPtr;

if (dequePtr -> count == 0)
{
fprintf(stderr, "Deque is empty!\n");
exit(1);
}

else
{
item = dequePtr -> rear -> entry;
newRearPtr = dequePtr -> front;

for (rearCount=dequePtr->count; rearCount>2; rearCount--)
{
newRearPtr = newRearPtr -> next;
}

dequePtr -> rear = newRearPtr;
free(newRearPtr -> next);
dequePtr -> count--;
}

return item;
}

/* Prints out the items in a Linked Deque */

void printDeque(Deque* dequePtr)
{
Node* currentNodePtr;
int itemCount;

printf("Deque:  ");

if (dequePtr -> count == 0)
{
printf("Deque empty...\n");
}

else
{
currentNodePtr = dequePtr -> front;

for (itemCount=dequePtr->count; itemCount>0; itemCount--)
{
printf("%d  ", currentNodePtr -> entry);

currentNodePtr = currentNodePtr -> next;
}

printf("\n");
}
}

void showMenu (void)
{
disp_open();
disp_move(0,0);
disp_eeop();
disp_close();

/*        clrscr();
*/
printf("Welcome to my little Deque manipulation thingy...\n");
printf("=================================================\n\n");
printf("1 Push\n2 Append\n3 Pop\n4 Eject\n5 Print\n");
printf("6 Size\n7 Clear screen/Show menu\n8 Quit\n\n");
printf("Enter option: ");
}

main()
{
int item, option;
Deque* theDeque;

initializeDeque(theDeque);

showMenu();

scanf("%d", &option);

while (option<1 && option>8)
{
printf("Not a vaild option... enter again: ");
scanf("%d", &option);
}


while (option!=8)
{
if (option==1)
{
printf("Please enter an integer to push...\n");

while (scanf("%d", &item) != EOF)
{
push(theDeque, item);

printDeque(theDeque);

printf("Keep pushing...(crtl-Z to exit): ");
}
}

else if (option==2)
{
printf("Please enter an integer to append...\n");

while (scanf("%d", &item) != EOF)
{
append(theDeque, item);

printDeque(theDeque);

printf("Keep appending...(crtl-Z to exit): ");
}
}

else if (option==3)
{
item = pop(theDeque);

printf("Popped: %d\n", item);
}

else if (option==4)
{
item = eject(theDeque);

printf("Ejected: %d\n", item);
}

else if (option==5)
{
printDeque(theDeque);
}

else if (option==6)
{
printf("Size: %d\n", theDeque -> count);
}

else if (option==7)
{
showMenu();
}

printf("Now what... ");
scanf("%d", &option);

while (option<1 && option>8)
{
printf("Not a vaild option... enter again: ");
scanf("%d", &option);
}
}

return 0;
}
**************************************************************************

Thanks

I'd try building it and debugging it under Win32 first, and then port it to DOS. It's much easier to chase down pointer bugs that way. -Walter

<tomohawk007@htomail.com> wrote in message news:a7uap2$55q$1@digitaldaemon.com...
> Hi there
>
> I just downloaded Digital Mars & am having problems testing it on a small
C
> program using DOS.  Other small programs seem to work but this one
doesn't.  The
> only difference is that this program uses the malloc() function.
>
> I am getting an access violation:
>
> ******************************************************
> Application exception occurred:
> App:  (pid=468)
> When: 28/03/2002 @ 16:19:37.957
> Exception number: c0000005 (access violation)
> ******************************************************
>
> Can you please tell me why this might be happening?
>
> Here is my program:
>
> ***********************************************************************
> /*  A program that initializes a Linked Deque & presents the user
> with a menu to manipulate the Linked Deque.
> Functions are included to: Push, Append, Pop, Eject, Print,
> Size, Show menu/Clear screen & Quit */
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <alloc.h>
> #include <conio.h>
> #include <disp.h>
>
>
> struct NodeRec
> {
> int entry;
> struct NodeRec* next;
> };
>
> typedef struct NodeRec Node;
>
> struct LinkedDequeRec
> {
> int count;
> Node* front;
> Node* rear;
> };
>
> typedef struct LinkedDequeRec Deque;
>
> /* Make a new node which contains a value */
>
> Node* makeNode (int value)
> {
> Node* newNodePtr = (Node*)malloc(sizeof(Node));
>
> if (newNodePtr == NULL)
> {
> fprintf(stderr, "Out of memory");
> exit(1);
> }
>
> else
> {
> newNodePtr -> entry = value;
> newNodePtr -> next = NULL;
> }
>
> return newNodePtr;
> }
>
> /* Initialize a Linked Deque to be empty */
>
> void initializeDeque (Deque* dequePtr)
> {
> dequePtr -> front = NULL;
> dequePtr -> rear = NULL;
> dequePtr -> count = 0;
> }
>
> /* Push an item at the front of a Linked Deque */
>
> void push (Deque* dequePtr, int item)
> {
> Node* newNodePtr = makeNode(item);
>
> if (newNodePtr != NULL)
> {
> if (dequePtr -> count == 0)
> {
> dequePtr -> front = newNodePtr;
> dequePtr -> rear = newNodePtr;
> dequePtr -> count = 1;
> }
>
> else
> {
> newNodePtr -> next = dequePtr -> front;
> dequePtr -> front = newNodePtr;
> dequePtr -> count++;
> }
> }
> }
>
> /* Append an item at the rear of a Linked Deque */
>
> void append (Deque* dequePtr, int item)
> {
> Node* newNodePtr = makeNode(item);
>
> if (newNodePtr != NULL)
> {
> if (dequePtr -> count == 0)
> {
> dequePtr -> front = newNodePtr;
> dequePtr -> rear = newNodePtr;
> dequePtr -> count = 1;
> }
>
> else
> {
> dequePtr -> rear -> next = newNodePtr;
> dequePtr -> rear = newNodePtr;
> dequePtr -> count++;
> }
> }
> }
>
> /* Pops an item off the front of the Deque & returns it */
>
> int pop (Deque* dequePtr)
> {
> int item;
> Node* oldNodePtr = dequePtr -> front;
>
> if (dequePtr -> count == 0)
> {
> fprintf(stderr, "Deque is empty!\n");
> exit(1);
> }
>
> else
> {
> item = oldNodePtr -> entry;
> dequePtr -> front = oldNodePtr -> next;
> free(oldNodePtr);
> dequePtr -> count--;
> }
>
> return item;
> }
>
> /* Ejects an item from the rear of the Deque & returns it */
>
> int eject (Deque* dequePtr)
> {
> int item, rearCount;
> Node* newRearPtr;
>
> if (dequePtr -> count == 0)
> {
> fprintf(stderr, "Deque is empty!\n");
> exit(1);
> }
>
> else
> {
> item = dequePtr -> rear -> entry;
> newRearPtr = dequePtr -> front;
>
> for (rearCount=dequePtr->count; rearCount>2; rearCount--)
> {
> newRearPtr = newRearPtr -> next;
> }
>
> dequePtr -> rear = newRearPtr;
> free(newRearPtr -> next);
> dequePtr -> count--;
> }
>
> return item;
> }
>
> /* Prints out the items in a Linked Deque */
>
> void printDeque(Deque* dequePtr)
> {
> Node* currentNodePtr;
> int itemCount;
>
> printf("Deque:  ");
>
> if (dequePtr -> count == 0)
> {
> printf("Deque empty...\n");
> }
>
> else
> {
> currentNodePtr = dequePtr -> front;
>
> for (itemCount=dequePtr->count; itemCount>0; itemCount--)
> {
> printf("%d  ", currentNodePtr -> entry);
>
> currentNodePtr = currentNodePtr -> next;
> }
>
> printf("\n");
> }
> }
>
> void showMenu (void)
> {
> disp_open();
> disp_move(0,0);
> disp_eeop();
> disp_close();
>
> /*        clrscr();
> */
> printf("Welcome to my little Deque manipulation thingy...\n");
> printf("=================================================\n\n");
> printf("1 Push\n2 Append\n3 Pop\n4 Eject\n5 Print\n");
> printf("6 Size\n7 Clear screen/Show menu\n8 Quit\n\n");
> printf("Enter option: ");
> }
>
> main()
> {
> int item, option;
> Deque* theDeque;
>
> initializeDeque(theDeque);
>
> showMenu();
>
> scanf("%d", &option);
>
> while (option<1 && option>8)
> {
> printf("Not a vaild option... enter again: ");
> scanf("%d", &option);
> }
>
>
> while (option!=8)
> {
> if (option==1)
> {
> printf("Please enter an integer to push...\n");
>
> while (scanf("%d", &item) != EOF)
> {
> push(theDeque, item);
>
> printDeque(theDeque);
>
> printf("Keep pushing...(crtl-Z to exit): ");
> }
> }
>
> else if (option==2)
> {
> printf("Please enter an integer to append...\n");
>
> while (scanf("%d", &item) != EOF)
> {
> append(theDeque, item);
>
> printDeque(theDeque);
>
> printf("Keep appending...(crtl-Z to exit): ");
> }
> }
>
> else if (option==3)
> {
> item = pop(theDeque);
>
> printf("Popped: %d\n", item);
> }
>
> else if (option==4)
> {
> item = eject(theDeque);
>
> printf("Ejected: %d\n", item);
> }
>
> else if (option==5)
> {
> printDeque(theDeque);
> }
>
> else if (option==6)
> {
> printf("Size: %d\n", theDeque -> count);
> }
>
> else if (option==7)
> {
> showMenu();
> }
>
> printf("Now what... ");
> scanf("%d", &option);
>
> while (option<1 && option>8)
> {
> printf("Not a vaild option... enter again: ");
> scanf("%d", &option);
> }
> }
>
> return 0;
> }
> **************************************************************************
>
> Thanks
>
>