Pushing data from a structure into a stack in C

The task of the program is to push all the dat开发者_运维技巧a from a structure into a stack, using memcpy. Upon execution, it successfully enters the data into the structure, but reaches a segmentation fault when it comes to the push() function.

Here's the code:

#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <mem.h>

typedef struct STD {
   char ime [50];
   int fn;
   float usp;
   } STD;


 typedef struct STACK {
    STD *s;
    STACK *next;

    } STACK;
  int push (void *a, int siz,  STACK **sst) {
STACK *snew;
snew = (STACK *) malloc (siz + 1);
memcpy (snew->s, a, siz); 
 snew -> next = *sst;
 *sst = snew;


 }

int main () {
STACK *st;
STD  ss;

printf ("Vyvedi ime");
gets (ss.ime);
ss.ime[49] = 0;
printf ("Vyvedi fn");
scanf ("%d", &ss.fn);

printf ("Vyvedi usp");
scanf ("%f", &ss.usp);



push (&ss, sizeof(ss) , &st);



system ("pause");      }

Don't know if it matters, I use DevC as a compiler.

This code is wrong:

STACK *snew;
snew = (STACK *) malloc (siz + 1);
memcpy (snew->s, a, siz); 

snew->s is not initialized when you memcpy a into it. I would expect to see two mallocs - one for STACK* and another for STD*, which you would then use to seed snew->s before copying stuff into it.

STACK *snew;
snew = (STACK *) malloc (sizeof(STACK));
snew->s = (STD*) malloc(sizeof(STD));
memcpy (snew->s, a, siz);

Alternatively you could use a single malloc, and point snew->s to the appropriate offset within it (after you've left space for the STACK struct).

STACK *snew;
snew = (STACK *) malloc (sizeof(STACK) + siz + 1);
snew->s = (char*)snew + sizeof(STACK);
memcpy (snew->s, a, siz);

The siz parameter on your push function seems superfluous, since you are always passing in a struct STD.

1. note you do not allocate a space for s
2. you need to initialize the st to NULL
3. pls check that snew is not NULL

i.e.

int push (void *a, int siz,  STACK **sst) {
  STACK *snew (STACK *) malloc (siz + 1);
  snew->s = (STD *) mallos (sizeof(STD)); // <-----------
  memcpy (snew->s, a, siz); 
  snew -> next = *sst;
  *sst = snew;
 }

And it looks like there are other issues there, start using meaningful names, not ss, st..

Here's what you do, Dalamar:
1. If you have a debugger, and you know how to use it, then step through the push() function to see where the segmentation fault occurs.
2. Otherwise, put a printf statement between every line in push():

printf ("1\n") ;  
...  
printf ("2\n") ;  
...  

This will also tell you where the segmentation fault occurs.
If you're still stuck, then get back to us with the new info.

#include <iostream>
#include <stdlib.h>
#include <conio.h>

#include "linkedlist.h"
int main(int argc, char *argv[])
{
 LinkedList myList;
 Node *node  ;
 int choice = 0 , index=0 ;
 string agentName, caseDesc ;
 int caseNo;
 do
 {

     cout<< "\n Enter 1 Add a new node to the end \n";
     cout<< " Enter 2 Add a new node to the beginning \n";
     cout<< " Enter 3 Print out the entire list \n";
     cout<< " Enter 4 Remove a node from the list \n";
     cout<< " Enter 5 Quit the program \n";
     cout<< " Enter your choice : ";
     cin>> choice;
     switch(choice){
       case 1:
                   //  Insert appropriate code here ....
       break;

       case 2:
                   //  Insert appropriate code here ....
       break;

       case 3:
                   //  Insert appropriate code here ....
       break;

       case 4:
                   //  Insert appropriate code here ....        
       break;

       case 5:
         exit(1);
       break;      

       default :
         cout<<"\n   Invalid Option, Please try again .....\n";
       break;

     }

 }while (true);




 system("PAUSE");   
 return 0;