fwrite() does not write data to file

[arnuld]

WANTED: Even if I do Ctrl-C in the middle of fgets(), fwrite() should
write the previously entered data to a file (except if I hit the file-size
limit)
PROBLEM: If I do a Ctrl-C in the middle of fgets(). fwrite() does not
write the data to the file.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

enum { INPUT_SIZE = 5 };
FILE* fp;

void write_to_file( const char* );
int main( void )
{
char arrc[INPUT_SIZE];

memset( arrc, '\0', INPUT_SIZE );

while( fgets(arrc, INPUT_SIZE, stdin) )
{
write_to_file( arrc );
}
return EXIT_SUCCESS;
}


void write_to_file( const char* arrc )
{
int arr_size;
long fwrite_bytes;

arr_size = strlen(arrc );
++arr_size;

if( ! (fp = fopen("zzz.txt" , "a")) )
{
perror("FOPEN ERROR\n");
exit( EXIT_FAILURE );
}

fwrite_bytes = fwrite( arrc, 1, arr_size, fp);

printf("fwrite_ bytes = %ld\n", fwrite_bytes);

if( arr_size != fwrite_bytes )
{
perror("FWRITE ERROR");
exit( EXIT_FAILURE );
}

/*
if( fclose(fp) )
{
perror("CLOSE ERROR\n");
}
*/
}
=============== OUTPUT =============== ======
[arnuld@dune CLS]$ gcc -ansi -pedantic -Wall -Wextra check_FILE_IO.c
[arnuld@dune CLS]$ ./a.out
lo
fwrite_bytes = 4

[arnuld@dune CLS]$ cat zzz.txt
[arnuld@dune CLS]$
In only these 3 cases, data gets written:

1) Remove the comments from the fclose(). I mean do a proper fclose().
2) You do proper exit using Ctrl-D.
3) User enters data more than the INPUT_SIZE.

but I don't want to close the file every time I have data. I want to keep
it open till I hit the size limit. The problem with fclose() is, if the
data entered is 2 bytes on each call, then it will take 500 openings and
closings, which will be very CPU intensive I think. I want this
program to be efficient in terms of CPU, memory is not the problem
here, I have got enough of it. I need to keep the file open but in doing
so a sudden quit using Ctrl-C discards everything user entered.
Any solution to the problem ?


--
www.lispmachine.wordpress.com
my email is @ the above blog.Google Groups is Blocked. Reason: Excessive Spamming

[vippstar]

On Sep 2, 10:50 am, arnuld <sunr...@invali d.addresswrote:

WANTED: Even if I do Ctrl-C in the middle of fgets(), fwrite() should
write the previously entered data to a file (except if I hit the file-size
limit)

PROBLEM: If I do a Ctrl-C in the middle of fgets(). fwrite() does not
write the data to the file.

^C typically kills the process. It's not possible to do what you want.

<snip>

[Keith Thompson]

arnuld <su*****@invali d.addresswrites :
[...]

but I don't want to close the file every time I have data. I want to keep
it open till I hit the size limit. The problem with fclose() is, if the
data entered is 2 bytes on each call, then it will take 500 openings and
closings, which will be very CPU intensive I think. I want this
program to be efficient in terms of CPU, memory is not the problem
here, I have got enough of it. I need to keep the file open but in doing
so a sudden quit using Ctrl-C discards everything user entered.
Any solution to the problem ?

fflush().

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Richard Heathfield]

arnuld said:

WANTED: Even if I do Ctrl-C in the middle of fgets(), fwrite() should
write the previously entered data to a file (except if I hit the
file-size limit)

Implementations are permitted to buffer streams, in which case an arbitrary
program termination may result in data in the buffer not being written to
the associated file.

To ensure (as far as possible, anyway) that data sent to fwrite is written
to the file, call fflush after fwrite:

fwrite_bytes = fwrite( arrc, 1, arr_size, fp);
if(fflush(fp) == EOF)
{
something went wrong

PROBLEM: If I do a Ctrl-C in the middle of fgets(). fwrite() does not
write the data to the file.

If you mean the data processed by previous fgets calls, fflush should fix
that.

If you mean data processed by /this/ fgets call, the one that you've just
interrupted, it isn't possible to do that in standard C - not even if you
mess with signal-handling - since there is no obligation on fgets to have
placed any data at all into your buffer at the point of interruption. It
only has to have done so by the time it returns, and it can't return (in
the normal sense) if you interrupt it.

--
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

[arnuld]

On Tue, 02 Sep 2008 08:13:07 +0000, Richard Heathfield wrote:

.... SNIP....

fwrite_bytes = fwrite( arrc, 1, arr_size, fp);
if(fflush(fp) == EOF)
{
something went wrong

If you mean the data processed by previous fgets calls, fflush should
fix that.

yes, I meant exactly that and hey... Richard, it works :)
--
www.lispmachine.wordpress.com
my email is @ the above blog.
Google Groups is Blocked. Reason: Excessive Spamming

[Joachim Schmitz]

vi******@gmail. com wrote:

On Sep 2, 10:50 am, arnuld <sunr...@invali d.addresswrote:

>WANTED: Even if I do Ctrl-C in the middle of fgets(), fwrite()
should write the previously entered data to a file (except if I hit
the file-size limit)

PROBLEM: If I do a Ctrl-C in the middle of fgets(). fwrite() does
not write the data to the file.

^C typically kills the process. It's not possible to do what you want.

^C typically (in UNIX) sends a SIGINT, which you could catch or even ignor.
But that would be off topic here...

Bye, Jojo

[Richard Heathfield]

Joachim Schmitz said:

vi******@gmail. com wrote:

>On Sep 2, 10:50 am, arnuld <sunr...@invali d.addresswrote:

>>WANTED: Even if I do Ctrl-C in the middle of fgets(), fwrite()
should write the previously entered data to a file (except if I hit
the file-size limit)

PROBLEM: If I do a Ctrl-C in the middle of fgets(). fwrite() does
not write the data to the file.

^C typically kills the process. It's not possible to do what you want.

^C typically (in UNIX) sends a SIGINT, which you could catch or even
ignor. But that would be off topic here...

Why? SIGINT is a standard signal. See 4.7 of C89 or 7.14 of C99.

--
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

[Joachim Schmitz]

Richard Heathfield wrote:

Joachim Schmitz said:

>vi******@gmail. com wrote:

>>On Sep 2, 10:50 am, arnuld <sunr...@invali d.addresswrote:
WANTED: Even if I do Ctrl-C in the middle of fgets(), fwrite()
should write the previously entered data to a file (except if I hit
the file-size limit)

PROBLEM: If I do a Ctrl-C in the middle of fgets(). fwrite() does
not write the data to the file.

^C typically kills the process. It's not possible to do what you
want.

^C typically (in UNIX) sends a SIGINT, which you could catch or even
ignor. But that would be off topic here...

Why? SIGINT is a standard signal. See 4.7 of C89 or 7.14 of C99.

Well, because I thought it to be POSIX.

Thanks for the correction.

Bye, Jojo

[vippstar]

On Sep 2, 7:31 pm, Richard Heathfield <[e-mail].i nvalidwrote:

Joachim Schmitz said:

vipps...@gmail. com wrote:

On Sep 2, 10:50 am, arnuld <sunr...@invali d.addresswrote:
WANTED: Even if I do Ctrl-C in the middle of fgets(), fwrite()
should write the previously entered data to a file (except if I hit
the file-size limit)

>PROBLEM: If I do a Ctrl-C in the middle of fgets(). fwrite() does
not write the data to the file.

^C typically kills the process. It's not possible to do what you want.

^C typically (in UNIX) sends a SIGINT, which you could catch or even
ignor. But that would be off topic here...

Why? SIGINT is a standard signal. See 4.7 of C89 or 7.14 of C99.

SIGINT is. What ^C does (or ^C itself) is not standard though. (not
even in POSIX)

[Harald van =?UTF-8?b?RMSzaw==?=]

On Tue, 02 Sep 2008 14:18:09 -0700, vippstar wrote:

On Sep 2, 7:31 pm, Richard Heathfield <[e-mail].i nvalidwrote:

>Joachim Schmitz said:

^C typically (in UNIX) sends a SIGINT, which you could catch or even
ignor. But that would be off topic here...

Why? SIGINT is a standard signal. See 4.7 of C89 or 7.14 of C99.

SIGINT is.

True, but it's worth pointing out that in ISO C, there is significantly
less that you are allowed to do in the signal handler.

What ^C does (or ^C itself) is not standard though. (not even
in POSIX)

<OTThat depends on what you mean. What ^C does is specified by POSIX,
but whether it is triggered by ^C is not. </OT>