function

[Bill Cunningham]

I am trying to write a utility that takes as argument 1 a file name to
write to and as argument 2 takes num as a number of zeros to write a
argument 1. A file of zeros. This is how far I have got. Why would I want a
file of zeros? To mount to a loopback device.

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

int
main (int argc, char *argv[])
{
if (argc != 3)
{
puts ("usage error");
exit (EXIT_FAILURE);
}
char a = '0';
int b, num;
FILE *fp;
num = atoi (argv[2]);
fp = fopen (argv[1], "wb");

I am thinking that I would need a for loop involved here somewhere. I am
not sure what to put in the body.

Bill

[Joachim Schmitz]

Re: function

Bill Cunningham wrote:

I am trying to write a utility that takes as argument 1 a file
name to write to and as argument 2 takes num as a number of zeros to
write a argument 1. A file of zeros. This is how far I have got. Why
would I want a file of zeros? To mount to a loopback device.

[OT]
dd if=/dev/zero of=<your filecount=<your size>
[/OT]

#include <stdio.h>
#include <stdlib.h>
>
int
main (int argc, char *argv[])
{
if (argc != 3)
{
puts ("usage error");
exit (EXIT_FAILURE);
}
char a = '0';

char a = '\0';

int b, num;
FILE *fp;
num = atoi (argv[2]);
fp = fopen (argv[1], "wb");
>
I am thinking that I would need a for loop involved here
somewhere. I am not sure what to put in the body.

while (num--)
fputc(a, fp);
fclose(fp);
return 0;
}

Still needs some error checking (num>=0, fp != NULL, fclose and fput worked)

Bill

Bye, Jojo

[Bill Cunningham]

Re: function


"Joachim Schmitz" <nospam.jojo@sc hmitz-digital.dewrote in message
news:g1rpes$mp7 $1@online.de...

[OT]
dd if=/dev/zero of=<your filecount=<your size>
[/OT]

Ah. The easy way out :)

>#include <stdio.h>
>#include <stdlib.h>
>>
>int
>main (int argc, char *argv[])
>{
> if (argc != 3)
> {
> puts ("usage error");
> exit (EXIT_FAILURE);
> }
> char a = '0';

char a = '\0';

Why the termination string character? Do you mean to replace my line or
are you adding one?

> int b, num;
> FILE *fp;
> num = atoi (argv[2]);
> fp = fopen (argv[1], "wb");
>>
> I am thinking that I would need a for loop involved here
>somewhere. I am not sure what to put in the body.

>
while (num--)
fputc(a, fp);
fclose(fp);
return 0;
}
>
Still needs some error checking (num>=0, fp != NULL, fclose and fput
worked)

I can get that part. I think.

>Bill

Bye, Jojo
>

[Bill Cunningham]

Re: function


"Joachim Schmitz" <nospam.jojo@sc hmitz-digital.dewrote in message
news:g1rpes$mp7 $1@online.de...

[snip]

while (num--) fputc(a, fp);
fclose(fp);
return 0;
}
>
Still needs some error checking (num>=0, fp != NULL, fclose and fput
worked)
>

>Bill

Bye, Jojo

While(num--) What's that? Is that the same as what I was thinking here.

int c;
for(c=1;c<num;c ++)

Bill

[Joachim Schmitz]

Re: function

Bill Cunningham wrote:

"Joachim Schmitz" <nospam.jojo@sc hmitz-digital.dewrote in message
news:g1rpes$mp7 $1@online.de...

>[OT]
>dd if=/dev/zero of=<your filecount=<your size>
>[/OT]

>
Ah. The easy way out :)

Jep 8-) Why reinventing the wheel...

>>#include <stdio.h>
>>#include <stdlib.h>
>>>
>>int
>>main (int argc, char *argv[])
>>{
>> if (argc != 3)
>> {
>> puts ("usage error");
>> exit (EXIT_FAILURE);
>> }
>> char a = '0';

>char a = '\0';

>
Why the termination string character?

It's not just that, it also is the nul character, a byte with all bits
unset.

Do you mean to replace my
line or are you adding one?

Replacing. Do you want zeros in the file or the ascii representation of the
charcter 0? I believe the earlier.

>> int b, num;
>> FILE *fp;
>> num = atoi (argv[2]);
>> fp = fopen (argv[1], "wb");
>>>
>> I am thinking that I would need a for loop involved here
>>somewhere. I am not sure what to put in the body.

>>
>while (num--)
> fputc(a, fp);
>fclose(fp);
>return 0;
>}
>>
>Still needs some error checking (num>=0, fp != NULL, fclose and fput
>worked)

>
I can get that part. I think.

Yep, left as an excercise to the reader 8-)

>>Bill

>Bye, Jojo

[Joachim Schmitz]

Re: function

Bill Cunningham wrote:

"Joachim Schmitz" <nospam.jojo@sc hmitz-digital.dewrote in message
news:g1rpes$mp7 $1@online.de...
>
[snip]
>

>while (num--) fputc(a, fp);
>fclose(fp);
>return 0;
>}
>>
>Still needs some error checking (num>=0, fp != NULL, fclose and fput
>worked)
>>

>>Bill

>Bye, Jojo

>
While(num--) What's that? Is that the same as what I was thinking
here.
int c;
for(c=1;c<num;c ++)

for(c=1;c<=num; c++) /* if you want to loop num times */
It's equivalent, just counting backwards and not needing yet another
variable

Bye, Jojo

[Bill Cunningham]

Re: function


"Joachim Schmitz" <nospam.jojo@sc hmitz-digital.dewrote in message
news:g1rq2v$nf9 $1@online.de...

[snip]

>>Still needs some error checking (num>=0, fp != NULL, fclose and fput
>>worked)

>>
> I can get that part. I think.

Yep, left as an excercise to the reader 8-)

Now here's what I tried in error checking that gave me a warning. I
must've messed up.

if((fputc(a,fp) )!=NULL)
if((fclose(fp)) !=NULL)

comparing argument with a without a cast or something like that the compiler
said. Without cast and comparing was mentioned by the compiler but it
compiled and didn't work. So I tried this.

if((fputc(a,fp) )==NULL)
puts("fputc error");

When I ran the binary fputc error was mentioned 10 times. My 2nd arg was 10.

Bill

[CBFalconer]

Re: function

Bill Cunningham wrote:

>

.... snip ...

>
While(num--) What's that? Is that the same as what I was thinking here.

That means while the expression num-- is non-zero, do the
following. The expression value is num before decrementing it.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.


** Posted from http://www.teranews.com **

[CBFalconer]

Re: function

Bill Cunningham wrote:

>

.... snip ...

>
comparing argument with a without a cast or something like that
the compiler said. Without cast and comparing was mentioned by
the compiler but it compiled and didn't work. So I tried this.
>
if((fputc(a,fp) )==NULL)
puts("fputc error");
>
When I ran the binary fputc error was mentioned 10 times. My
2nd arg was 10.

Look up what a function does and returns before you use it. In
this case:

7.19.7.3 The fputc function

Synopsis
[#1]
#include <stdio.h>
int fputc(int c, FILE *stream);

Description

[#2] The fputc function writes the character specified by c
(converted to an unsigned char) to the output stream pointed
to by stream, at the position indicated by the associated
file position indicator for the stream (if defined), and
advances the indicator appropriately. If the file cannot
support positioning requests, or if the stream was opened
with append mode, the character is appended to the output
stream.

Returns

[#3] The fputc function returns the character written. If a
write error occurs, the error indicator for the stream is
set and fputc returns EOF.

Note the returned value.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.


** Posted from http://www.teranews.com **

[santosh]

Re: function

Bill Cunningham wrote:

<snip>

Now here's what I tried in error checking that gave me a warning.
must've messed up.
>
if((fputc(a,fp) )!=NULL)

If you read your system's documentation for fputc you'll find that it
returns either the character passed (as an int) or EOF on error. NULL
is the wrong value to be comparing with. The above is better written
as:

if (fputc(ch, stream) == EOF) {
/* error */
}

if((fclose(fp)) !=NULL)

Again, fclose will return EOF on failure.

<snip>

[Bill Cunningham]

Re: function


"santosh" <santosh.k83@gm ail.comwrote in message
news:g1s4e8$igh $3@registered.m otzarella.org.. .

Bill Cunningham wrote:
>
<snip>
>

> Now here's what I tried in error checking that gave me a warning.
> must've messed up.
>>
>if((fputc(a,fp ))!=NULL)

>
If you read your system's documentation for fputc you'll find that it
returns either the character passed (as an int) or EOF on error. NULL
is the wrong value to be comparing with. The above is better written
as:
>
if (fputc(ch, stream) == EOF) {
/* error */
}
>

>if((fclose(fp) )!=NULL)

>
Again, fclose will return EOF on failure.
>
<snip>

I usually don't miss these things in error checking. I was suprised when
it didn't work but I guess I've had NULL on my mind. Earlier in this post I
wanted to write zeros to a file and found out the proper use was with the
string terminating character '\0' which is a byte with all the bits turned
off. Now a questions about the *putc functions. Do they take and write a
char or 8 bits, or an unsigned int? Fputc's first parameter is an int and I
declared an int and gave it the value of '\0'. If the char is taken from the
first int parameter why an int instead of a char? Is more information needed
than the char itself like padding or the like?

Bill

[Bill Cunningham]

Re: function


"CBFalconer " <cbfalconer@yah oo.comwrote in message
news:48417EB4.1 B3F9B56@yahoo.c om...

[snip]

That means while the expression num-- is non-zero, do the
following. The expression value is num before decrementing it.
>

conditionals. One of my weak points now. I can barely use while. I have
for and it down well. Switch is unusable and unreadable to me at this point.

Bill

[Richard]

Re: function

"Bill Cunningham" <nospam@nspam.c omwrites:

"CBFalconer " <cbfalconer@yah oo.comwrote in message
news:48417EB4.1 B3F9B56@yahoo.c om...
>
[snip]
>

>That means while the expression num-- is non-zero, do the
>following. The expression value is num before decrementing it.
>>

conditionals. One of my weak points now. I can barely use while. I have
for and it down well. Switch is unusable and unreadable to me at this point.
>
Bill

"while" is about 3x easier to understand than "for". See if you can see why.

[santosh]

Re: function

Bill Cunningham wrote:

>
"santosh" <santosh.k83@gm ail.comwrote in message
news:g1s4e8$igh $3@registered.m otzarella.org.. .

>Bill Cunningham wrote:
>>
><snip>
>>

>> Now here's what I tried in error checking that gave me a
>> warning. must've messed up.
>>>
>>if((fputc(a,f p))!=NULL)

>>
>If you read your system's documentation for fputc you'll find that it
>returns either the character passed (as an int) or EOF on error. NULL
>is the wrong value to be comparing with. The above is better written
>as:
>>
> if (fputc(ch, stream) == EOF) {
> /* error */
> }
>>

>>if((fclose(fp ))!=NULL)

>>
>Again, fclose will return EOF on failure.
>>
><snip>

>
I usually don't miss these things in error checking. I was
suprised when
it didn't work but I guess I've had NULL on my mind. Earlier in this
post I wanted to write zeros to a file and found out the proper use
was with the string terminating character '\0' which is a byte with
all the bits turned off.

Not necessarily. It's just a byte with value zero.

Now a questions about the *putc functions. Do
they take and write a char or 8 bits, or an unsigned int?

They take an int and a FILE * parameter and they attempt to write the
int parameter, cast to an unsigned char, to the stream indicated. A
char is commonly, but not necessarily eight bits. It's needs to be at
least eight bits, but could be more, as in the Cray or in most DSPs.

Fputc's
first parameter is an int and I declared an int and gave it the value
of '\0'. If the char is taken from the first int parameter why an int
instead of a char? Is more information needed than the char itself
like padding or the like?

This is I think just for compatibility with fgetc.

[Richard]

Re: function

santosh <santosh.k83@gm ail.comwrites:

Bill Cunningham wrote:
>

>>
>"santosh" <santosh.k83@gm ail.comwrote in message
>news:g1s4e8$ig h$3@registered. motzarella.org. ..

>>Bill Cunningham wrote:
>>>
>><snip>
>>>
>>> Now here's what I tried in error checking that gave me a
>>> warning. must've messed up.
>>>>
>>>if((fputc(a, fp))!=NULL)
>>>
>>If you read your system's documentation for fputc you'll find that it
>>returns either the character passed (as an int) or EOF on error. NULL
>>is the wrong value to be comparing with. The above is better written
>>as:
>>>
>> if (fputc(ch, stream) == EOF) {
>> /* error */
>> }
>>>
>>>if((fclose(f p))!=NULL)
>>>
>>Again, fclose will return EOF on failure.
>>>
>><snip>

>>
> I usually don't miss these things in error checking. I was
> suprised when
>it didn't work but I guess I've had NULL on my mind. Earlier in this
>post I wanted to write zeros to a file and found out the proper use
>was with the string terminating character '\0' which is a byte with
>all the bits turned off.

>
Not necessarily. It's just a byte with value zero.

Why on earth would you say that? It serves ZERO purpose whatsoever to
someone with such obvious difficulties as Bill.. All you will do is
confuse the guy more.

>

>Now a questions about the *putc functions. Do
>they take and write a char or 8 bits, or an unsigned int?

>
They take an int and a FILE * parameter and they attempt to write the
int parameter, cast to an unsigned char, to the stream indicated. A
char is commonly, but not necessarily eight bits. It's needs to be at
least eight bits, but could be more, as in the Cray or in most DSPs.

Ditto. Refer the man to the man page or whatever.