james@dlss2.UUCP (James Cummings) (11/02/90)
I have been struggling with what ought to be an easy problem.
I am trying to build a Last In First Out stack that I can store the
several structures in. I want to be able to "pop" them back out again
in reverse order.
So far, with a structure like:
struct myst {
char word1[10];
char word2[10];
struct myst *next;
};
and some pointers of the same form, I have only managed to retreive
the last structure on the stack...I seem to be able to go no further.
Could some kind sole, please nudge me in the right direction or
give me a *pointer to a book?
Env: Sys V 3.2.1
K&R Ccdm@gem-hy.Berkeley.EDU (Dale Cook) (11/03/90)
In article <111@dlss2.UUCP>, james@dlss2.UUCP (James Cummings) writes: |> |> I have been struggling with what ought to be an easy problem. |> I am trying to build a Last In First Out stack that I can store the |> several structures in. I want to be able to "pop" them back out again |> in reverse order. |> So far, with a structure like: |> struct myst { |> char word1[10]; |> char word2[10]; |> struct myst *next; |> }; |> and some pointers of the same form, I have only managed to retreive |> the last structure on the stack...I seem to be able to go no further. |> |> Could some kind sole, please nudge me in the right direction or ^^^^^^^^^ You want a gentle kick? Or maybe a friendly fish? [couldn't resist...] |> give me a *pointer to a book? Given the structure you have defined, and no information on how you are using it, I can only guess that your problem is that you have defined a stack structure with only one entry. Are you allocating storage for each stack entry as you need it? If not, you need to, or else pick an arbitrary stack maximum and preallocate your structure as an array. ---------------------------------------------------------------------- --- Dale Cook "In order to comprehend the infinite, one need only consider man's capacity for stupidity" --- Edward Abbey ---------------------------------------------------------------------- Lengthy disclaimer follows; press 'n' to skip... ========== long legal disclaimer follows, press n to skip =========== ^L Neither the United States Government or the Idaho National Engineering Laboratory or any of their employees, makes any warranty, whatsoever, implied, or assumes any legal liability or responsibility regarding any information, disclosed, or represents that its use would not infringe privately owned rights. No specific reference constitutes or implies endorsement, recommendation, or favoring by the United States Government or the Idaho National Engineering Laboratory. The views and opinions expressed herein do not necessarily reflect those of the United States Government or the Idaho National Engineering Laboratory, and shall not be used for advertising or product endorsement purposes.
Ingo.Wilken@arbi.informatik.uni-oldenburg.de (Ingo Wilken) (11/07/90)
james@dlss2.UUCP (James Cummings) writes: > struct myst { > char word1[10]; > char word2[10]; > struct myst *next; > }; > and some pointers of the same form, I have only managed to retreive ^^^^^^^^^^^^ >the last structure on the stack...I seem to be able to go no further. You only need one pointer, the stackbase. All you need to do is store a new item on the stack as the first item in the linked list. So if you push item1, item2, item3 on the stack, the list looks like this: empty stack: stackbase -> NULL push item1 : stackbase -> item1 -> NULL push item2 : stackbase -> item2 -> item1 -> NULL push item3 : stackbase -> item3 -> item2 -> item1 -> NULL pop item3 : stackbase -> item2 -> item1 -> NULL Well, here a the "standard" stack routines: -----cut here----- struct myst *stackbase = (struct myst *) NULL; push( char *word1, char *word2 ) { struct myst *help; help = (struct myst *) malloc( sizeof(struct myst) ); if( help == (struct myst *) NULL ) /* out of memory */ else { strcpy( help->word1, word1 ); strcpy( help->word2, word2 ); help->next = stackbase; stackbase = help; } } char * tos_word1() /* top of stack */ { if( stackbase == (struct myst *) NULL ) /* stack is empty */ else return( stackbase->word1 ); } /* the same thing again for tos_word2() */ pop() { struct myst *help; if( stackbase == (struct myst *) NULL ) /* stack is empty */ else { help = stackbase; stackbase = stackbase->next; free( (void *) help ); } } -----cut here----- Hope this helps, Ingo -- Ingo Wilken, CS Student, Univ. of Oldenburg, W-Germany * IRC-Nickname: Nobody ----------------------+ Ingo.Wilken@arbi.informatik.uni-oldenburg.de My opinions may have | wilken@uniol.UUCP (..!uunet!unido!uniol!wilken) changed, but not the | wilken%arbi.informatik.uni-oldenburg.de@DOLUNI1.BITNET fact that I am right! | wilken@uniol.ZER * Voice: +049 04461 80800 (Weekends)