cat

[Jag]

I've read parts of K&R's ANSI C v2 and this is what their cat looked
like but when I compared the speed of this code to gnu cat, it seems
very slow. How do I optimize this for greater speeds? is there an
alternative algorithm?

void catfile(FILE *in, FILE *out) {
register int num_char;

/*Get characters*/
while ((num_char = getc(in)) != EOF) {
/*Print to standard output*/
putc(num_char, out);
}
}

Thanks.

[Micah Cowan]

Jag <ta*******@gmai l.comwrites:

I've read parts of K&R's ANSI C v2 and this is what their cat looked
like but when I compared the speed of this code to gnu cat, it seems
very slow. How do I optimize this for greater speeds? is there an
alternative algorithm?

void catfile(FILE *in, FILE *out) {
register int num_char;

/*Get characters*/
while ((num_char = getc(in)) != EOF) {
/*Print to standard output*/
putc(num_char, out);
}
}

This example was intended to be just that: an example. It gives a
clear, concise method for copying in to out.

If you look at GNU cat's source code, you'll see that it's nowhere
near as clear and concise (this is due in no small part to the fact
that it has to do a good deal more than the above example does,
including some options that require a bit of processing on the input).

POSIX systems that support the thread-safety option have to lock the
I/O streams every time you call getc() or putc(). On such systems,
getc_unlocked() and putc_unlocked() (POSIX options, not Standard C)
will usually be notably faster. Some implementations also provide
other means for using the "unlocked" versions.

Other common techniques would be to read in larger blocks at a time,
or perhaps to avoid the Standard C buffered I/O calls and use POSIX
read(), write() (it's unclear to me how much better that is than to
use setvbuf() to turn off buffering and use fwrite() and fread(),
which is a good option if you'd like to stick to Standard C).

Taking a look at the source code for GNU cat and other similar
utilities like dd, for (Unix-specific) ideas on how to improve
efficiency.

--
HTH,
Micah J. Cowan
Programmer, musician, typesetting enthusiast, gamer...
http://micah.cowan.name/

[CBFalconer]

Jag wrote:

>
I've read parts of K&R's ANSI C v2 and this is what their cat
looked like but when I compared the speed of this code to gnu
cat, it seems very slow. How do I optimize this for greater
speeds? is there an alternative algorithm?

void catfile(FILE *in, FILE *out) {
register int num_char;

/*Get characters*/
while ((num_char = getc(in)) != EOF) {
/*Print to standard output*/
putc(num_char, out);
}
}

You may find the following faster:

void catfile(FILE *in, FILE *out) {
int ch;

while (EOF != (ch = getc(in))) putc(out, ch);
}

If so, consider why.

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

--
Posted via a free Usenet account from http://www.teranews.com

[Eric Sosman]

CBFalconer wrote:

Jag wrote:

>I've read parts of K&R's ANSI C v2 and this is what their cat
looked like but when I compared the speed of this code to gnu
cat, it seems very slow. How do I optimize this for greater
speeds? is there an alternative algorithm?

void catfile(FILE *in, FILE *out) {
register int num_char;

/*Get characters*/
while ((num_char = getc(in)) != EOF) {
/*Print to standard output*/
putc(num_char, out);
}
}

You may find the following faster:

void catfile(FILE *in, FILE *out) {
int ch;

while (EOF != (ch = getc(in))) putc(out, ch);
}

If so, consider why.

I don't see why it would be faster. As far as I can
tell, the only substantive change is the removal of
`register', which is unlikely to make a difference --
and if it does make a difference, it's likely to make
the revised code slower, not faster.

(Well, there's one other "speed improvement," and it
could be a large one: Code that doesn't compile uses very
little execution time! Have another look at the putc()
call ...)

--
Eric Sosman
es*****@ieee-dot-org.invalid

[Gerry Ford]

Ohimigod!

I am recently given to understand that cat means something other than
one-half of the dead felines in arbitrary buckets.

I sense that you drank of the forbidden K&R chapter, forbidden, not by these
jerks but by the standard, Dan Pop, Elvis, and me.

--
Gerry Ford

"Er hat sich georgiert." Der Spiegel, 2008, sich auf Chimpy Eins komma null
beziehend.
"Eric Sosman" <es*****@ieee-dot-org.invalidwrot e in message
news:k8******** *************** *******@comcast .com...

CBFalconer wrote:

>Jag wrote:

>>I've read parts of K&R's ANSI C v2 and this is what their cat
looked like but when I compared the speed of this code to gnu
cat, it seems very slow. How do I optimize this for greater
speeds? is there an alternative algorithm?

void catfile(FILE *in, FILE *out) {
register int num_char;

/*Get characters*/
while ((num_char = getc(in)) != EOF) {
/*Print to standard output*/
putc(num_char, out);
}
}

You may find the following faster:

void catfile(FILE *in, FILE *out) {
int ch;

while (EOF != (ch = getc(in))) putc(out, ch);
}

If so, consider why.

I don't see why it would be faster. As far as I can
tell, the only substantive change is the removal of
`register', which is unlikely to make a difference --
and if it does make a difference, it's likely to make
the revised code slower, not faster.

(Well, there's one other "speed improvement," and it
could be a large one: Code that doesn't compile uses very
little execution time! Have another look at the putc()
call ...)

--
Eric Sosman
es*****@ieee-dot-org.invalid

[Micah Cowan]

Richard <de***@gmail.co mwrites:

And on that subject I often find
it pays dividends in the maintenance stakes to always bracket off the
body of conditions even if they are only one line e.g

,----
| while(c){
| c=do(c);
| }
`----

You state that it pays dividends, but neglect to state how/why.

I'm guessing you mean that, if you have:

while(c)
c=do(c);

And then later want to add another statement in the while's body, then
you have to go through the tedium of adding braces first.

If that's what you mean, then my answer is:
- It's not appreciably harder to add braces later than it is to put
them in in the first place.
- In a decent editor, such as emacs or vim, it's simple to define a
new macro to automatically add (or remove) braces for one-line
bodies.

--
Micah J. Cowan
Programmer, musician, typesetting enthusiast, gamer...
http://micah.cowan.name/

[Richard Heathfield]

Micah Cowan said:

<snip>

I'm guessing you mean that, if you have:

while(c)
c=do(c);

And then later want to add another statement in the while's body, then
you have to go through the tedium of adding braces first.

That isn't the issue. If the compound statement has two statements, you
need the braces anyway, and it doesn't make a lot of odds whether you add
them now or later. In fact, if that *were* the only issue, deferring them
could save you (a miniscule amount of) work.

If that's what you mean, then my answer is:
- It's not appreciably harder to add braces later than it is to put
them in in the first place.

Agreed. BUT - it is appreciably harder to remember to add them later on
special occasions than to put them in every time as a matter of habit.

- In a decent editor, such as emacs or vim, it's simple to define a
new macro to automatically add (or remove) braces for one-line
bodies.

That's as maybe, but it isn't the work of adding such tools - it's the work
of remembering to use them. Unless, of course, by "automatic" you really
do mean automatic!! :-)

--
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

[Micah Cowan]

Richard Heathfield <rj*@see.sig.in validwrites:

>If that's what you mean, then my answer is:
- It's not appreciably harder to add braces later than it is to put
them in in the first place.

Agreed. BUT - it is appreciably harder to remember to add them later on
special occasions than to put them in every time as a matter of habit.

Hm. I haven't found it to be so.

while (c)
c=do_it(c);
c=do_another_th ing(c);

looks too broken right away for me not to notice it (though, perhaps
now that I'm doing more Python coding work these days, that may
change?).

I used to actually always put the braces in. I've fallen out of that
practice, just because I find it slightly more readable without, for
one-line bodies.

--
Micah J. Cowan
Programmer, musician, typesetting enthusiast, gamer...
http://micah.cowan.name/

[Jag]

On Mar 6, 11:08 am, Micah Cowan <mi...@holliste r.bcsweb.comwro te:

Jag <talon....@gmai l.comwrites:

I've read parts of K&R's ANSI C v2 and this is what their cat looked
like but when I compared the speed of this code to gnu cat, it seems
very slow. How do I optimize this for greater speeds? is there an
alternative algorithm?

void catfile(FILE *in, FILE *out) {
register int num_char;

/*Get characters*/
while ((num_char = getc(in)) != EOF) {
/*Print to standard output*/
putc(num_char, out);
}
}

This example was intended to be just that: an example. It gives a
clear, concise method for copying in to out.

If you look at GNU cat's source code, you'll see that it's nowhere
near as clear and concise (this is due in no small part to the fact
that it has to do a good deal more than the above example does,
including some options that require a bit of processing on the input).

POSIX systems that support the thread-safety option have to lock the
I/O streams every time you call getc() or putc(). On such systems,
getc_unlocked() and putc_unlocked() (POSIX options, not Standard C)
will usually be notably faster. Some implementations also provide
other means for using the "unlocked" versions.

Other common techniques would be to read in larger blocks at a time,
or perhaps to avoid the Standard C buffered I/O calls and use POSIX
read(), write() (it's unclear to me how much better that is than to
use setvbuf() to turn off buffering and use fwrite() and fread(),
which is a good option if you'd like to stick to Standard C).

Taking a look at the source code for GNU cat and other similar
utilities like dd, for (Unix-specific) ideas on how to improve
efficiency.

--
HTH,
Micah J. Cowan
Programmer, musician, typesetting enthusiast, gamer...http://micah.cowan.name/

Thanks!

[regis]

Micah Cowan wrote:

Richard Heathfield <rj*@see.sig.in validwrites:

>>>If that's what you mean, then my answer is:
- It's not appreciably harder to add braces later than it is to put
them in in the first place.

Agreed. BUT - it is appreciably harder to remember to add them later on
special occasions than to put them in every time as a matter of habit.

Hm. I haven't found it to be so.

while (c)
c=do_it(c);
c=do_another_th ing(c);

looks too broken right away for me not to notice it (though, perhaps
now that I'm doing more Python coding work these days, that may
change?).

while (c);
c= do_it(c);

the error above is harder to find than:

while (c);{
c= do_it(c);
}

you cannot miss the ';' between ')' and '{':
it is not a natural location for it, and in fact,
for this very reason, you'll rarely find such a code.

But the first mistake is often found in the code of
my students. And when they ask why their code does not work
as expected, you may have a hard time before catching
the extra semi-colon.