C code to implement file locking?

Answer 1

#include <stdio.h>

#include <errno.h>

#include <fcntl.h>

int fd;

/* file descriptor */ char *filename;

main(argc,

argv)

int argc;

char *argv[];

{ extern

void exit(), perror();

/* get database file name from command line and open the * file for read and write access. */ if (argc

< 2) { (void) fprintf(stderr,

"usage: %s filename\n",

argv[0]); exit(2); } filename

=

argv[1]; fd

=

open(filename,

O_RDWR);

if (fd

< 0) { perror(filename);

exit(2); } }