问文件锁定程序没有锁定文件

EN

#include <stdio.h>
#include <stdlib.h>
#include <sys/file.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>


int controller, fsize;
char data[1000], ch;
int fd ;
                  /* l_type, l_whence, l_start, l_len, l_pid*/
struct flock fl = {F_UNLCK, SEEK_SET,    0,       0,      0};
void Edit();
void Delete();
void Exit();
void Lock();


void main()
{

do
{
    clrscr();
    fd = open("demo.txt", "w");
    FILE *fp = fdopen("demo.txt", "w");
    if (fd != NULL)
    {
        printf("Opening the file!\n");
        fd = fdopen("demo.txt", "r");
        printf("We can open the file in write mode, meaning no other process has lock enabled on it.");
        printf("Contents of the file are: \n\t");
        readfile(fd);
        fclose(fd);
    }
    else if ((fd = fopen("demo.txt", "r"))!= NULL)
    {
        fd = fopen("demo.txt", "r");
        printf("We can open the file in read mode, meaning some other process has locked the write permissions on it.");
        printf("Contents of the file are: \n\t");
        readfile(fd);
        fclose(fd);
    }
    else
    {
        printf("File does not exist.\n");
    }
    printf("\n\t\t***** WELCOME USER! THIS IS A SIMPLE TEXT EDITOR *****");

    Lock();
    Operations();
}
while(1);
}

void Lock()
{
fd = fopen("demo.txt", "w");
fl.l_type = F_RDLCK;
fl.l_pid = getpid();
if (fcntl(fd, F_SETLK, &fl) == -1)
{
    printf("Can't set exclusive lock\n");
}
else if(fl.l_type!=F_UNLCK)
{
    printf("File has been exclusively locked by the process %d\n", fl.l_pid);
    fl.l_type = F_UNLCK;
    printf("File Unlocked! Other processes can execute on the file now.");
}
else
{
    printf("File is not locked\n");
}
fclose(fd);
}

void clrscr()
{
system("@cls||clear");
}

void Operations()
{
    printf("\n\n\tOperations you can perform here:\n\t\n");
    printf("\n\t1.ADD TO FILE\n\t2.DELETE THE FILE\n\t3.EXIT\n");
    printf("\n\tEnter your choice: ");
    scanf("%d",&controller);
    switch(controller)
    {
    case 1:
        Add();
        break;
    case 2:
        remove("demo.txt");
        break;
    case 3:
        exit(0);
    }
}



void Add()
{
    fd = fopen("demo.txt", "a");
    printf("Enter contents to store in file : \n");
    fgets(data, 1000, stdin);
    fputs(data, fd);
    fclose(fd);
    printf("Data added to the file successfully");
    fd = fopen("demo.txt", "r");
    readfile(fd);
    fclose(fd);
}



void readfile(FILE *fPtr)
{
char c = getc(fd);
while (c != EOF)
{
    printf("%c", c);
    c = getc(fd);
}
}