/* opener.c - Example of how a number of programs (all copies of this one)
 *            can share a file with the first one initializing the content 
 *            of the file.
 *            
 */
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <errno.h>
#include <string.h>

extern int errno;

#define LINEMAX 256

int main()
{
  int fd;
  char line[LINEMAX];
  char *datum = "rosanna\n";
  char *filename = "moo.foo";
  int n;
  
  // If file does not exist, create it,
  // write something to it, and close it.
  if ((fd = open(filename, O_RDWR | O_CREAT | O_EXCL, 
		 S_IRWXU | S_IRWXG | S_IRWXO )) >= 0) {
    // if it does not exist, create it, write something to it,
    // and close it.
    printf("%s already exists\n", filename);
    write(fd, datum, strlen(datum));
    close(fd);
  } else {
    if (errno != EEXIST) {
      perror("Cannot create file");
      exit(1);
    }
    printf("%s already exists\n", filename);
  } 

  // Open the file
  if ((fd = open(filename, O_RDWR)) < 0) {
    perror("Error opening an existing file");
    exit(1);
  }

  // Read and print out file's content
  while ((n = read(fd, line, strlen(datum))) > 0) {
    line[n-1] = '\0';
    printf("line = %s\n", line);
  }    
  close(fd);
  return(0);
}