Question

I’m working on an easy project but I’ve encountered an error. I’m coding in Unix and executing the code with the terminal.

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main()
{
    int atis;
    char *weather;

    //Création du fichier ATIS
    if((atis = creat("atis", 0666)) == -1)
    {
        printf("Error while creating the ATIS file\n");
        exit(-1);
    }

    //Ouverture du fichier ATIS
    if((atis = open("atis", 0666)) == -1)
    {
        printf("Permission denied\n");
        exit(-1);
    }

    //Mise à jour du fichier ATIS
    printf("OK or KO for a take-off? ");
    gets(weather);
    if(write(atis, weather, sizeof(weather))==-1)
    {
        printf("Write error\n");
        exit(-1);
    }


    close(atis);
    return 0;
}**

The error is a segmentation fault 11.

Thank you in advance!
(and sorry for my English, it’s really bad ^^)

Answer 1

The problem is these two lines:

char *weather;

and

gets(weather);

The first declares weather to be a pointer, but it’s left uninitialized (i.e. points to a seemingly random location). The second line writes to what weather points to, which means you write to some random location.

Declare weather as an array, and use fgets instead:

char weather[64];

/* ... */

fgets(weather, sizeof(weather), stdin);