[Beds] Programming

[David Pashley]

On Jan 28, 2006 at 13:07, Stephen Elliott praised the llamas by saying:
> Hi,
> 
> Thanks a lot for that info, kinda makes some sense now.
> 
> There are two other small programs that I have attached to this mail that
> also use system calls. If you have a chance please could you do the same for
> these.

The second does what it says in the comments at the top and the third
has no chance of compiling. None of the code you've sent to the list are
exactly what I'd call shining examples of programming.


I highly recommend you buy a decent book on
learning C. The Oreilly one might be good; they usually are.
Alternatively, The C Programming Language (2nd Edition) by Brian W.
Kernighan and Dennis Ritchie.
> 
> Many Thanks
> Steve...
> 
> 
> 
> On Jan 27, 2006 at 19:00, Stephen Elliott praised the llamas by saying:
> > Hi,
> >
> > I have a C program here which a friend has sent me and I am trying to
> > understand. I did basic C programming when I was at college and wrote
> quite
> > a nice Shipbourne radar system, but this one blows me.
> >
> > It uses pointers and I understand the principle behind them. I was
> wondering
> > if someone could explain the code to me, the line I am having the most
> > trouble with is the calloc line.
> >
> 
> It's worth pointing out this is really bad C, but lets go through it:
> 
>  | #include <fcntl.h>
> 
>  have no idea why this is imported. You want unistd.h (for read) and
>  stdio.h (for printf).
>  |
>  | main()
> 
> Start the main() function. This should really be "int main(void)" or
> "int main(int argc, char *argv[])".
>  | {
>  |
>  | char *c; int fd, sz; c = (char *) calloc(100, sizeof(char));
> 
> Defines a dynamic character array, and two integers (fd and sz) and then
> allocates memory for 100 chars.
> 
>  | fd = open("in1", O_RDONLY);
>  |
> Open a file called in1 for reading.
> 
>  | 	if (fd < 0)
>  | 	{
>  | 		perror("r1");
>  | 		exit(1);
>  | 	}
>  |
> Check for errors opening the file.
> 
>  | sz = read(fd, c, 10);
> 
> Read 10 bytes from the file and put the number of bytes read into sz.
> 
>  | printf("called read(%d, c, 10). returned that %d bytes were read.\n", fd,
> sz);
> 
> Output how many bytes were read.
> 
>  | c[sz] = '\0';
>  |
> Null terminate the current end of the string so we can output it.
> 
>  | printf("Those bytes are as follows: %s\n", c);
>  |
> Output the bytes read.
> 
>  | sz = read(fd, c, 99);
>  |
> Read in 99 bytes.
> 
>  | printf("called read(%d, c, 99). returned that %d bytes were read.\n",fd,
> sz);
>  |
> Again print out how many bytes we read.
> 
>  | c[sz] = '\0';
> 
> null-terminate the string again
> 
>  | printf("Those bytes are as follows: %s\n", c);
> 
> print out those bytes.
> 
>  | close(fd);
> 
> Close the file.
> 
>  | }
> 
> End of the function and program.
> 




-- 
David Pashley
david at davidpashley.com
Nihil curo de ista tua stulta superstitione.