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#ifndef lint
static char *rcs = "$Header: stack.c,v 1.1 88/01/15 13:05:28 simpson Rel $";
#endif
/*
$Log: stack.c,v $
* Revision 1.1 88/01/15 13:05:28 simpson
* initial release
*
* Revision 0.1 87/12/11 18:31:20 simpson
* beta test
*
*/
/* Generalized stack manipulation routines. Routines provided are:
*
* char *push(p)
* char *p;
*
* Pushes the stack with the data in pointer p. Space is not allocated
* for the data; that is, the data is by reference. Consequently, you should
* not delete the data until you have popped it from the stack. A pointer to
* the passed data is returned. NULL is returned if memory could not be
* allocated to push the data. If the data passed is larger than
* elementsize, then only elementsize bytes will be copied. If it is
* smaller, you will probably get a segmentation violation.
*
* char *pop()
*
* Pops the stack and returns the popped value. If the stack is empty, NULL
* is returned.
*
* Implementation rationale: We don't copy data by value since we would have
* trouble popping the data. When we pop data, we want to free its space but
* we also want to return the data popped. We could store the data in a
* temporary buffer of the element size but it would get written over with
* every pop. Also, copying by value slows things down.
*/
#include <local/standard.h>
#define NULL 0
/* Represent the stack as a linked list of elements */
static struct element {
char *data; /* Pointer to actual data */
struct element *next; /* Pointer to next element down */
} *Head;
/* Push the stack */
char *push(data)
char *data;
{
struct element *p;
char *malloc();
if (!data || !(p = (struct element *)malloc((unsigned)sizeof(struct
element))))
return NULL;
p->next = Head, Head = p;
p->data = data;
return data;
}
/* Pop the stack */
char *pop()
{
char *p;
struct element *ep;
if (!Head)
return NULL;
p = Head->data;
ep = Head;
Head = Head->next;
free((char *)ep);
return p;
}
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