simple c linux programing question

itz2000 · 11-03-2007, 03:22 PM

I just don't get why I can't write to the file I create using open with the filedescriptor I received ?

Code:

#include <stdio.h>
#include <unistd.h> // write syscall
#include <fcntl.h> // Open syscall
#include <sys/types.h>
#include <sys/stat.h>
int main ()
{
	const char *strPath = "/path/to/test.check";
	int nfd = open(strPath, O_CREAT | O_APPEND, S_IRUSR | S_IRGRP | S_IROTH | S_IWUSR | S_IWGRP | S_IWOTH);
	ssize_t ssWriteResponse = write(nfd,"Hello World",12);
	int nCloseRV = close(nfd);
	return 0;
}

File is being created, but the write doesn't work...

Thanks for your help.

SciYro · 11-03-2007, 03:57 PM

You dont dident open the file for writing. Also, "Hellow World" is only 11 characters.

Code:

{
	const char *strPath = "Mytest";
	int nfd = open(strPath, O_CREAT | O_APPEND | O_RDWR, S_IRUSR | S_IRGRP | S_IROTH | S_IWUSR | S_IWGRP | S_IWOTH);
	write(nfd,"Hello World",11);
	close(nfd);
	return 0;
}

itz2000 · 11-03-2007, 04:59 PM

Quote:

Originally Posted by SciYro

You dont dident open the file for writing. Also, "Hellow World" is only 11 characters.

Code:

{
	const char *strPath = "Mytest";
	int nfd = open(strPath, O_CREAT | O_APPEND | O_RDWR, S_IRUSR | S_IRGRP | S_IROTH | S_IWUSR | S_IWGRP | S_IWOTH);
	write(nfd,"Hello World",11);
	close(nfd);
	return 0;
}

THanks DUDE!
Havn't noticed that..

also, about the 12, yeah, I've noticed it just now, anyways what I'm really doing is write(nfd,strWriteToFile,strlen(strWriteToFile)); so I don't have to recount every time the string is changed.

Thanks!

itz2000 · 12-23-2007, 03:17 PM

sorry for being lame, but can u see the problem here?

Code:

#ifdef HAVE_CONFIG_H
#include <config.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#endif

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

int main(int argc, char *argv[])
{
	
	int fd = open("/home/zuki/script.ini",O_RDONLY);
	char *buf;
	buf = "";
	size_t rval;
	size_t wval;
       	while ((rval = read(fd, &buf, 14)) != EOF)
			{
				if ((wval = write(1, buf, rval))!=rval)
				{
					char *buf = "An error has occured, returning";
					write(2,buf,strlen(buf));
					return(1);
				}
			}

	return(0);
}

THANKS

ta0kira · 12-23-2007, 04:45 PM

There's no storage associated with buf; it's merely a value that currently denotes a null string literal. There's no place for the read data to be placed. You either need to make buf a char[14] or use malloc.
ta0kira