segmentation err in switch case

Question

I wrote a code to implement file locking in c. After resolving a errors and ignoring all the warnings haha, I was able to compile the code but now the thing is, When I try to add content to the file, it is showing segmentation error. code is:

#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>

char data[1000], ch;
int cont;
int main(int argc, char **argv) {
if (argc > 1) {
int fd = fopen(argv[1], "w");
if(fd == -1) {
  printf("Unable to open the file\n");
  exit(1);
}
static struct flock lock;

lock.l_type = F_WRLCK;
lock.l_start = 0;
lock.l_whence = SEEK_SET;
lock.l_len = 0;
lock.l_pid = getpid();

int ret = fcntl(fd, F_SETLKW, &lock);
printf("Return value of fcntl:%d\n",ret);
printf("\n\n\tOperations you can perform here:\n\t\n");
printf("\n\t1.ADD TO FILE\n\t2.DELETE THE FILE\n\t3.PRINT CONTENTS OF FILE\n\t4.EXIT");
printf("\n\tEnter your choice: ");
scanf("%d",&cont);
switch(cont)
    {
    case 1:
        printf("Enter contents to store in file : \n");
        fgets(data, 1000, stdin);
        fputs(data, fd);
        printf("Data added to the file successfully");
        break;
    case 2:
        remove(fd);
        break;
    case 3:
        int c = getc(fd);
        while (c != EOF)
        {
            printf("%c", c);
            c = getc(fd);
        }
    case 4:
        exit(0);
    }
}
}

I even tried doing

fclose(fd); fd = fopen("advisory.txt","a");

this, at the beginning of the switch case to add content to file. But to no avail.

Answer 1

You are confusing file descriptors (as returned by open()) with pointers-to-FILE (as returned by fopen()). Don't put diesel in the tank of a car that needs regular.

Now what?

Read the manual pages for both functions and understand the differences. Understand what is meant by the Standard I/O Library in C and the functions it provides (e.g. fopen(), fgets(), fgetc(), fclose() and many more). Understand what Unix I/O functions are (e.g. open(), read(), write(), close()). Then you will be able to correct the many problems in your code leading to the segfault.