using system call

ej25 · 11-30-2004, 09:47 AM

hi

any process has three standard descriptor:0,1 and 2. for example the printf() library function always sends its output using file descriptor 1 which display screen

in my code I'm trying to read a file and display it without using the C library function. I use the write system call to write the file to the screen

Code:

int fd1 = open(argv[c], O_RDONLY); 
int n,i;
char buffer[SIZE];
while ((n=read(fd1, buffer, SIZE)) != 0) {
		for (i=0; i<n ; i++)
		 write(stdout , buffer[i], sizeof(buffer));

	}

I want to take it line by line and display it. So, What am I doing? why there is no output ?

jlliagre · 11-30-2004, 10:04 AM

write(fileno(stdout), ...)
or
write(1,...)

ej25 · 11-30-2004, 10:32 AM

thanks jlliagre

I already solve it

but it give me this

---------------------------------------------------------------------------------------------------------------------------
int fd1 = open(argv[c], O_RDONLY);
int n,i;
char buffer[SIZE];
while ((n=read(fd1, buffer, SIZE)) != 0) {
for (i=0; i<n ; i++)
write(stdout , buffer[i], sizeof(buffer));

}
n Apr 8 19:37:14 EDT 2001i586ccse)}@ô÷ÿ¿¸U@0ùÿ¿lZ@÷ÿ¿["úÿ¿¬"@÷ÿ¿/"
----------------------------------------------------------------------------------------------------------------------------
and in some file it display correctly and it display part of again, I don't why
is it the size?

perfect_circle · 11-30-2004, 10:48 AM

stdout, stdin etc are stream descriptors (FILE *)

Quote:

I'm trying to read a file and display it without using the C library function

it's probably non of my bussiness but why are you doing this?

perfect_circle · 11-30-2004, 10:58 AM

Code:

 write(stdout , buffer[i], sizeof(buffer));

first of all the file descripor for stdout is 1 (i think)

2. use sizeof(char)
sizeof(buffer) is SIZE*sizeof(char), and on every write() u write only buffer[i] which is a character not a string

instead of

Code:

 for (i=0; i<n ; i++)
 write(1 , buffer[i], sizeof(char));

you may also try

Code:

write(1, buffer, n)

I think this should work, but i'm not sure.
you may try it

ej25 · 11-30-2004, 10:58 AM

Quote:

it's probably non of my bussiness but why are you doing this?

I solve it in regular way. But I want to do it in the hard way to learn better and to minimize my code

Is there a way to take it character by character and display each character alone like this:

Code:

while ((n=read(fd1, buffer, SIZE)) != 0) {
for (i=0; i<n ; i++)
		 write(1, buffer[i], sizeof(buffer));
	}

jlliagre · 11-30-2004, 10:59 AM

Quote:

I already solve it

Not sure you solved it, as you didn't change your code.
You seem to have redefined stdout as an int equal to 1 which is a very bad initiative ...
here is something that should work:

Code:

while ((n=read(fd1, buffer, SIZE)) != 0)
{
  write(1 , buffer, n);
}

ej25 · 11-30-2004, 11:26 AM

Quote:

Your seems to have redefined stdout as an int equal to 1 which is a very bad initiative ...

what do you mean by "bad initiative"?

Code:

while ((n=read(fd1, buffer, SIZE)) != 0){
write(1 , buffer, n);
}

I try by using this code to take it character by character it dosen't work, why?

jlliagre · 11-30-2004, 11:31 AM

Quote:

what do you mean by "bad initiative"?

Bad initiative because, as perfect_circle already pointed out, stdout is already defined as a pointer (i.e. the address of something) while the write call is expecting a file descriptor which is an integer.
If you redeclare well known variables to mean something different, your code is going to be unreadable.

perfect_circle already replied about how to output one character after another, which is also, sorry to tell, a very bad initiative, unless you are competing for the slowest program contest ...

ej25 · 11-30-2004, 11:45 AM

Thanks all

I really Benefit for what you said