Question

I am trying to compile my code but I am not able to compile it. I am using VS 2010 and I get this message:

‘Tel_zoznam.exe’: Loaded ‘C:\Windows\SysWOW64\msvcr100d.dll’, Symbols loaded.
Run-Time Check Failure #3 – The variable ‘p_prvy’ is being used without being initialized.

It stops at p_prvy->next = NULL;

Here is my code:

#include "stdafx.h"

#define MAX 31

typedef struct ZOZNAM{
    char meno[MAX];
    char priezvisko[MAX];
    char cislo1[MAX];
    char cislo2[MAX];
    char cislo3[MAX];
    struct ZOZNAM *next;
} ZOZNAM;

int main(void){
    char c;
    ZOZNAM * p_prvy;
ZOZNAM * p_akt;
    p_prvy->next = NULL;
    int z;
    p_akt=p_prvy;

    printf(" Pre pridanie kontaktu do zoznamu stlacte 'p'\n Pre vypis zoznamu zadajte 'v'\n Pre ukoncenie programu zadajte 'k'\n");
    z=pocet_zaznamov();
    printf("%d",z);
    while(1==1){
        scanf("%c",&c);

        switch(c){
            case 'p': vlozit(p_akt); break;
            case 'v': vypis(p_prvy); break;
            case 'n': nacitanie(p_akt); break;
        }
    }
    return 0;
}

Answer 1

In your main() function, you have the following declaration of the p_prvy variable:

ZOZNAM * p_prvy;

Almost immediately after that, you say:

p_prvy->next = NULL;

Which means you are using p_prvy variable. However, it is not being initialized and so has unspecified value. This is called Undefined Behavior, or simply UB.

What you need to do is initialize that pointer. For example, by allocating some memory:

ZOZNAM * p_prvy = (ZOZNAM *)malloc(sizeof(ZOZNAM));

You may also have it initialized to NULL, but then dereferencing NULL will take your process down.