Thread: Need help with write function

Hi,
I wrote this small piece of code to test the effect of O_DIRECT flag. But for some strange reason the program fails at the write function line with invalid argument. I cant seem to inderstand why it is failing to write. Could anyone please suggest what I am doing wrong.

I am passing a writable file to to at time of invocation.

Thanks.

Code:

#define _GNU_SOURCE
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <string.h>

void usage(char *command)
{

	fprintf(stderr,"usage: %s FILENAME\n", command);
	exit(1);
}

int main(int argc, char *argv[])
{

	char *filename;
	int fd;
	char buf[15] = {0};

	if(argc != 2) usage(argv[0]);

	filename = argv[1];

	fd = open(filename, O_CREAT | O_DIRECT | O_RDWR, 0666);

	if (fd < 0) {

		fprintf(stderr, "ERROR: failed to open `%s': %s \n",
                             filename, strerror(errno));
                exit(1);

	}



	/* invoke the write system call . Not actually writing anything */
	if((write(fd, &buf[0], sizeof(buf[0]) * 15)) == -1) {

		fprintf(stderr, "Error writing to file:%s \n", strerror(errno));
		close(fd);
		exit(1);
	}

	
	close(fd);

	return 0;

}