Unexpected Output when reading a files using read()

[Sanchit]

My program is

#include <fcntl.h>
#include <unistd.h>
int main(void)
{
int fd;
ssize_t nread;
char buf[100];
/*open file for reading */
fd = open("marks.dat ", O_RDONLY);
/* read the data */
nread = read(fd, buf, 1024);
/*close the file */

printf("%s\n\n" ,buf);
close(fd);
}

And my marks.dat is
123 123 123 4 56 sas as fd faa a s d sf d!!f d fd f df df d(HERE FILE
ENDS)

Output is
123 123 123 4 56 sas as fd faa a s d sf d!!f d fd f df df d
Ȭ¿^äì·9 ÷·ž–ž± ¬Â¿XƒôÏú ·Å¾Â–ر¬¿ )Â…


I am unable to understand why these special symbols are coming

[Morris Dovey]

Re: Unexpected Output when reading a files using read()

Sanchit wrote:

>
My program is
>
#include <fcntl.h>
#include <unistd.h>
int main(void)
{
int fd;
ssize_t nread;
char buf[100];
/*open file for reading */
fd = open("marks.dat ", O_RDONLY);
/* read the data */
nread = read(fd, buf, 1024);
/*close the file */
>
printf("%s\n\n" ,buf);
close(fd);
}
>
And my marks.dat is
123 123 123 4 56 sas as fd faa a s d sf d!!f d fd f df df d(HERE FILE
ENDS)
>
Output is
123 123 123 4 56 sas as fd faa a s d sf d!!f d fd f df df d
Ã^¬¿^äì·9 ÷·žÂ-ž±¬¿XÂf ôÃ?ú·žÂ-Ã~±¬¿)Â?
>
I am unable to understand why these special symbols are coming

The %s specification in printf() caused printing of the data at
buf until a '\0' was found. What do you suppose would have
happened if no terminator at all had been found?

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

http://www.iedu.com/DeSoto/

[maxim.pgv]

Re: Unexpected Output when reading a files using read()

On 21 мар, 12:49, Sanchit <sanchitgupt... @gmail.comwrote :

Output is
123 123 123 4 56 sas as fd faa a s d sf d!!f d fd f df df d
Ȭ¿^äì·9 ÷·ž– ž±¬¿Xƒ ôÏú·ž– ر¬¿)…
>
I am unable to understand why these special symbols are coming

Try to clear your buffer:

memset( buf, 0, sizeof(buf) );

[Ben Bacarisse]

Re: Unexpected Output when reading a files using read()

Richard Heathfield <rjh@see.sig.in validwrites:

Sanchit said:
>

>My program is
>>
>#include <fcntl.h>
>#include <unistd.h>

<snip>

Alternative solution: after the read() call, test nread to see whether the
call worked. If so, and if nread is < 100, you can just do this:
>
buf[nread] = {0};

Typo: you meant

buf[nread] = 0;

(or maybe = '\0').

To the OP: in addition to what has been said, you must include stdio.h
to make the use of printf well-defined.

--
Ben.

[Richard Heathfield]

Re: Unexpected Output when reading a files using read()

Ben Bacarisse said:

Richard Heathfield <rjh@see.sig.in validwrites:
>

>[...] if nread is < 100, you can just do this:
>>
> buf[nread] = {0};

>
Typo: you meant
>
buf[nread] = 0;
>
(or maybe = '\0').

Ta.

To the OP: in addition to what has been said, you must include stdio.h
to make the use of printf well-defined.

Ooooh, ta twicely.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[jacob navia]

Re: Unexpected Output when reading a files using read()

Richard Heathfield wrote:

Ben Bacarisse said:
>

>Richard Heathfield <rjh@see.sig.in validwrites:
>>

>>[...] if nread is < 100, you can just do this:
>>>
>> buf[nread] = {0};

>Typo: you meant
>>
> buf[nread] = 0;
>>
>(or maybe = '\0').

>
Ta.
>

>To the OP: in addition to what has been said, you must include stdio.h
>to make the use of printf well-defined.

>
Ooooh, ta twicely.
>

Yeah. Always so fast to see a missing
'L'
when writing an integer constant, then blaming people for that.

Note: You should read your code before you post!


--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique

http://www.cs.virginia.edu/~lcc-win32

[Richard Heathfield]

Re: Unexpected Output when reading a files using read()

jacob navia said:

Richard Heathfield wrote:

>Ben Bacarisse said:
>>

>>Richard Heathfield <rjh@see.sig.in validwrites:
>>>
>>>[...] if nread is < 100, you can just do this:
>>>>
>>> buf[nread] = {0};
>>Typo: you meant
>>>
>> buf[nread] = 0;
>>>
>>(or maybe = '\0').

>>
>Ta.
>>

>>To the OP: in addition to what has been said, you must include stdio.h
>>to make the use of printf well-defined.

>>
>Ooooh, ta twicely.
>>

>
Yeah. Always so fast to see a missing
'L'
when writing an integer constant, then blaming people for that.

I don't know what you're talking about. I haven't blamed anyone for missing
an L suffix.

Note: You should read your code before you post!

Well, I do - I read it while I'm writing it. But I don't claim to be
perfect, and I do make mistakes. When that happens, I fess up. It is a
strategy that I recommend highly.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Keith Thompson]

Re: Unexpected Output when reading a files using read()

Sanchit <sanchitgupta.1 @gmail.comwrite s:

My program is
>
#include <fcntl.h>
#include <unistd.h>
int main(void)
{
int fd;
ssize_t nread;
char buf[100];
/*open file for reading */
fd = open("marks.dat ", O_RDONLY);
/* read the data */
nread = read(fd, buf, 1024);
/*close the file */
>
printf("%s\n\n" ,buf);
close(fd);
}

[snip]

In addition to the other comments (attempting to read 1024 bytes into
a 100-byte buffer, printing with "%s" something that isn't a string,
and the missing "#include <stdio.h>"), you might consider using the
standard C functions (fopen, fread, fclose) rather than the
POSIX-specific ones you're using (open, read, close). There are times
when the POSIX functions have advantages over the corresponding
standard C functions, but I don't see any indication that this is one
of those times.

--
Keith Thompson (The_Other_Keit h) <kst-u@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"