working with stack in C - c

Question

I am trying to implement the following functionality
It takes a line of string as input and then tokenizes them and put them in a stack and later on it prints the buffer reverse
"welcome to the den"
whould show up as
den the to welcome
the problem with what I have so far is that it stops working and after debugging I realize that in the push function called in the main , the value of the token is not getting passed to the function .
Can any one please help me with why it does not pass the string of token to the push function .
I think there is some thing wrong with "char* data;" in the struct
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
// self-referential structure
struct stackNode
{
char* data;
struct stackNode *pNext;
};
typedef struct stackNode StackNode;
typedef StackNode *StackNodePtr;
// function prototypes
void push( StackNodePtr *pTop, char value );
//int pop( StackNodePtr *pTop );
//int isEmpty( StackNodePtr pTop );
void printStack( StackNodePtr pCurrent );
int main( void )
{
char *pToken = NULL;
int counter;
char input[BUFFER_SIZE];
StackNodePtr pStack = NULL;
printf("Please enter a line of text here :\n");
gets(input);
pToken = strtok(input, " ");
while(pToken != NULL)
{
push(&pStack, pToken);
printf("%p '%s'\n", pToken, pToken);
pToken = strtok(NULL, " ");
}
printf("I am out of while loop");
printStack(pStack);
return 0;
}
// Insert a node at the stack top
void push( StackNodePtr *pTop, char* value )
{
StackNodePtr pNew;
pNew = malloc( sizeof( StackNode ) );
if ( pNew != NULL )
{
pNew->data = value;
pNew->pNext = *pTop; // insert at top of stack
*pTop = pNew;
}
else
{
printf( "%d not inserted. No memory available.\n", value );
}
}
// output stack contents to the console
void printStack( StackNodePtr pCurrent )
{
if ( pCurrent == NULL )
{
printf( "The stack is empty.\n\n" );
}
else
{
printf( "The stack is:\n" );
while ( pCurrent != NULL )
{
printf( "%s", pCurrent->data );
pCurrent = pCurrent->pNext; // move to next element
}
printf( "NULL\n\n" );
}
}

Answer 1

This works:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define BUFFER_SIZE 256
// self-referential structure
struct stackNode
{
char* data;
struct stackNode *pNext;
};
typedef struct stackNode StackNode;
typedef StackNode *StackNodePtr;
// function prototypes
void push(StackNodePtr* pTop, char* value);
//int pop( StackNodePtr *pTop );
//int isEmpty( StackNodePtr pTop );
void printStack( StackNodePtr pCurrent );
int main( void )
{
char *pToken = NULL;
int counter;
char input[BUFFER_SIZE];
StackNodePtr pStack = NULL;
printf("Please enter a line of text here :\n");
gets(input);
pToken = strtok(input, " ");
while(pToken != NULL)
{
push(&pStack, pToken);
printf("%p '%s'\n", pToken, pToken);
pToken = strtok(NULL, " ");
}
printf("I am out of while loop");
printStack(pStack);
return 0;
}
// Insert a node at the stack top
void push( StackNodePtr* pTop, char* value )
{
StackNodePtr pNew;
pNew = (StackNode*)malloc( sizeof( StackNode ) );
if ( pNew != NULL )
{
pNew->data = value;
pNew->pNext = *pTop; // insert at top of stack
*pTop = pNew;
}
else
{
printf( "%s not inserted. No memory available.\n", value );
}
}
// output stack contents to the console
void printStack( StackNodePtr pCurrent )
{
if ( pCurrent == NULL )
{
printf( "The stack is empty.\n\n" );
}
else
{
printf( "The stack is:\n" );
while ( pCurrent != NULL )
{
printf( "%s", pCurrent->data );
pCurrent = pCurrent->pNext; // move to next element
}
printf( "NULL\n\n" );
}
}
Input:
welcome to the den
Output:
0x7fff31d13fc0 'welcome'
0x7fff31d13fc8 'to'
0x7fff31d13fcb 'the'
0x7fff31d13fcf 'den'
I am out of while loopThe stack is:
denthetowelcomeNULL
I really only modified the code to compile on a reasonable machine. Just make sure you aren't printing character arrays as decimal types. I didn't fix any other issues, so no guarantees, just that THIS bit compiles and runs. I'm assuming you are going to add onto it later. Just make sure you are tracking your memory allocations.

Answer 2

I suspect the main problem is the mismatch between the prototype for push and it's definition.
void push( StackNodePtr *pTop, char value );
Vs
void push( StackNodePtr *pTop, char *value )
When I tried to compile the original it would not even compile, but maybe some broken would compile it and perhaps ignore the definition.
Here is a working version with the only change being to assign the declaration with the definition. Note that there are a shedload of warnings - you should address these as well.