right padding

[marc]

Hello,

Is it possible to right pad with "0" (or other character != blank) ?
for example :
1 , length 10 ="1000000000 "
I've tried with sprintf but I can only left pad with "0" or right pad
with blanks =>
"0000000001 "
"1 "

Thanks.

[Richard Heathfield]

Re: right padding

marc said:

Hello,
>
Is it possible to right pad with "0" (or other character != blank) ?
for example :
1 , length 10 ="1000000000 "
I've tried with sprintf but I can only left pad with "0" or right pad
with blanks =>
"0000000001 "
"1 "

sprintf doesn't let you choose the padding character. But it's pretty easy
to write a function to do the padding for you:

#include <stdio.h>
#include <assert.h>
#include <limits.h>

char *pad(char *s, int n, size_t width, int padch)
{
int count = 0;
char *t = s;
assert(width (sizeof n * CHAR_BIT + 5) / 3);
count = sprintf(t, "%d", n);
t += count;
while(count < len)
{
*t++ = padch;
}
*t = '\0';
return s;
}

In keeping with the spirit of comp.lang.c, the above is untested (because
I'm in a hurry).

--
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

[s0suk3@gmail.com]

Re: right padding

On Oct 21, 4:17 am, Richard Heathfield <rjh@see.sig.in validwrote:

marc said:
>

Hello,

>

Is it possible to right pad with "0" (or other character != blank) ?
for example :
1 , length 10 ="1000000000 "
I've tried with sprintf but I can only left pad with "0" or right pad
with blanks =>
"0000000001 "
"1         "

>
sprintf doesn't let you choose the padding character. But it's pretty easy
to write a function to do the padding for you:
>
#include <stdio.h>
#include <assert.h>
#include <limits.h>
>
char *pad(char *s, int n, size_t width, int padch)
{
  int count = 0;
  char *t = s;
  assert(width (sizeof n * CHAR_BIT + 5) / 3);

What's the purpose of this? Let's say that int is four bytes long. The
expression on the right side of the '>' will yield 37 / 3 (12). What
does 'width' represent? (You aren't using it anywhere else in the
function.)

  count = sprintf(t, "%d", n);
  t += count;
  while(count < len)

'len' is undefined.

  {
    *t++ = padch;
  }

And that will yield an infinite loop.

  *t = '\0';
  return s;
>
}
>
In keeping with the spirit of comp.lang.c, the above is untested (because
I'm in a hurry).

Here's a safer and tested version:

char *PadSnprintf(ch ar *str, // the buffer
int n, // sizeof(str)
int item, // the item to convert
char paddingChar) // the padding character
{
snprintf(str, n, "%d", item);

char *p = str + strlen(str);
while (p < str + n - 1)
*p++ = paddingChar;

*p = '\0';
return str;
}

Sebastian

[Richard Heathfield]

Re: right padding

s0suk3@gmail.co m said:

On Oct 21, 4:17 am, Richard Heathfield <rjh@see.sig.in validwrote:

<snip>

>assert(width (sizeof n * CHAR_BIT + 5) / 3);

>
What's the purpose of this? Let's say that int is four bytes long. The
expression on the right side of the '>' will yield 37 / 3 (12).

No, for four-byte ints it yields *at least* 12. If bytes are wider than
eight bits, which is legal, it will give a larger value.

What does 'width' represent?

It represents the width of the buffer starting at s. It must be big enough
to hold the text representation of an integer. If int is four octets in
size, then it could hold a value whose base ten text representation is as
large as -2147483648, which is eleven bytes long, so the buffer must be at
least twelve bytes long (one for the null terminator).

(You aren't using it anywhere else in the function.)

I did mean to use it...

>count = sprintf(t, "%d", n);
>t += count;
>while(count < len)

>
'len' is undefined.

....here. I meant width, not len.

>

>{
>*t++ = padch;
>}

>
And that will yield an infinite loop.

Well, now you're just being picky. :-)

Here's a safer and tested version:
>
char *PadSnprintf(ch ar *str, // the buffer
int n, // sizeof(str)

If the comment is correct, why do you need n? Why not just use sizeof(str)?
But I suspect the comment is wrong.

int item, // the item to convert
char paddingChar) // the padding character
{
snprintf(str, n, "%d", item);

Right away, your "safer and tested version" fails to link on a vast number
of C installations that don't have access to snprintf.

The two bugs that you spotted in my code (and I thank you for that) are
trivial to fix. It's rather less trivial to implement snprintf on systems
that lack 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

[s0suk3@gmail.com]

Re: right padding

On Oct 21, 1:59 pm, Richard Heathfield <rjh@see.sig.in validwrote:

s0suk3@gmail.co m said:

On Oct 21, 4:17 am, Richard Heathfield <rjh@see.sig.in validwrote:
(You aren't using it anywhere else in the function.)

>
I did mean to use it...
>

count = sprintf(t, "%d", n);
t += count;
while(count < len)

>

'len' is undefined.

>
...here. I meant width, not len.
>

{
*t++ = padch;
}

>

And that will yield an infinite loop.

>
Well, now you're just being picky.  :-)

A bit :-) Well, even if you would have used 'width' instead of 'len',
'count' isn't being incremented anywhere.

Here's a safer and tested version:

>

char *PadSnprintf(ch ar *str,         // the buffer
                  int n,             // sizeof(str)

>
If the comment is correct, why do you need n? Why not just use sizeof(str)?
But I suspect the comment is wrong.

Perhaps the comment is a bit misleading. The confusion is that if you
have an array declared like 'char str[10];', sizeof(str) will yield
10, whereas sizeof(str) inside PadSnprintf() will only yield the size
of a pointer (4 bytes or so), regardless of the size of the array to
which it points.

                  int item,          // theitem to convert
                  char paddingChar)  // the paddingcharacte r
{
    snprintf(str, n, "%d", item);

>
Right away, your "safer and tested version" fails to link on a vast number
of C installations that don't have access to snprintf.
>
The two bugs that you spotted in my code (and I thank you for that) are
trivial to fix. It's rather less trivial to implement snprintf on systems
that lack it.

Well, I wouldn't call them "a vast number." Even some non-C99
compilers support it (e.g., MSVC++).

Sebastian

[Richard Heathfield]

Re: right padding

s0suk3@gmail.co m said:

On Oct 21, 1:59 pm, Richard Heathfield <rjh@see.sig.in validwrote:

>s0suk3@gmail.co m said:

<snip>

Here's a safer and tested version:

>>

char *PadSnprintf(ch ar *str, // the buffer
int n, // sizeof(str)

>>
>If the comment is correct, why do you need n? Why not just use
>sizeof(str)? But I suspect the comment is wrong.

>
Perhaps the comment is a bit misleading. The confusion is that if you
have an array declared like 'char str[10];', sizeof(str) will yield
10, whereas sizeof(str) inside PadSnprintf() will only yield the size
of a pointer (4 bytes or so),

Or 1, or 2, or whatever. Yes.

regardless of the size of the array to which it points.

It doesn't point to an array. It points to the first member of an array.

int item, // the item to convert
char paddingChar) // the padding character
{
snprintf(str, n, "%d", item);

>>
>Right away, your "safer and tested version" fails to link on a vast
>number of C installations that don't have access to snprintf.
>>
>The two bugs that you spotted in my code (and I thank you for that) are
>trivial to fix. It's rather less trivial to implement snprintf on
>systems that lack it.

>
Well, I wouldn't call them "a vast number."

I have quite a few implementations installed on various bits of kit around
here, and only *one* of them provides snprintf (and only when invoked in
non-conforming mode, and with different semantics to C99).

Even some non-C99 compilers support it (e.g., MSVC++).

I checked. My copy doesn't.

Obviously the call is legal C99. And C99, like the Ritz Hotel, is open to
all.

--
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

[CBFalconer]

Re: right padding

s0suk3@gmail.co m wrote:

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

.... snip ...

>

>If the comment is correct, why do you need n? Why not just use
>sizeof(str)? But I suspect the comment is wrong.

>
Perhaps the comment is a bit misleading. The confusion is that if
you have an array declared like 'char str[10];', sizeof(str) will
yield 10, whereas sizeof(str) inside PadSnprintf() will only yield
the size of a pointer (4 bytes or so), regardless of the size of
the array to which it points.

However you can apply the esoteric strlen(s) function to get the
length of the passed string.

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

[Ben Bacarisse]

Re: right padding

CBFalconer <cbfalconer@yah oo.comwrites:

s0suk3@gmail.co m wrote:

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

... snip ...

>>

>>If the comment is correct, why do you need n? Why not just use
>>sizeof(str) ? But I suspect the comment is wrong.

>>
>Perhaps the comment is a bit misleading. The confusion is that if
>you have an array declared like 'char str[10];', sizeof(str) will
>yield 10, whereas sizeof(str) inside PadSnprintf() will only yield
>the size of a pointer (4 bytes or so), regardless of the size of
>the array to which it points.

>
However you can apply the esoteric strlen(s) function to get the
length of the passed string.

That's unlikely to be useful in this case. The pointer need not point
at a string -- in fact it would very unusual to require that a
function of this sort be passed a pointer to string.

--
Ben.

[Richard Heathfield]

Re: right padding

CBFalconer said:

s0suk3@gmail.co m wrote:

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

... snip ...

>>

>>If the comment is correct, why do you need n? Why not just use
>>sizeof(str) ? But I suspect the comment is wrong.

>>
>Perhaps the comment is a bit misleading. The confusion is that if
>you have an array declared like 'char str[10];', sizeof(str) will
>yield 10, whereas sizeof(str) inside PadSnprintf() will only yield
>the size of a pointer (4 bytes or so), regardless of the size of
>the array to which it points.

>
However you can apply the esoteric strlen(s) function to get the
length of the passed string.

What passed string?

Has it ever occurred to you to read threads before trying to participate in
them?

--
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

[CBFalconer]

Re: right padding

Richard Heathfield wrote:

CBFalconer said:

>s0suk3@gmail.co m wrote:

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

>... snip ...

>>>
>>>If the comment is correct, why do you need n? Why not just use
>>>sizeof(str )? But I suspect the comment is wrong.
>>>
>>Perhaps the comment is a bit misleading. The confusion is that
>>if you have an array declared like 'char str[10];', sizeof(str)
>>will yield 10, whereas sizeof(str) inside PadSnprintf() will
>>only yield the size of a pointer (4 bytes or so), regardless of
>>the size of the array to which it points.

>>
>However you can apply the esoteric strlen(s) function to get the
>length of the passed string.

>
What passed string?
>
Has it ever occurred to you to read threads before trying to
participate in them?

The following was the function under discussion. If str is not a
string, it should be. Do try to control your love of petty
objections.

>>>>char *PadSnprintf(ch ar *str, // the buffer

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

[Richard Heathfield]

Re: right padding

CBFalconer said:

Richard Heathfield wrote:

>CBFalconer said:

>>s0suk3@gmail.co m wrote:
>>>Richard Heathfield <rjh@see.sig.in validwrote:
>>>>
>>... snip ...
>>>>
>>>>If the comment is correct, why do you need n? Why not just use
>>>>sizeof(str) ? But I suspect the comment is wrong.
>>>>
>>>Perhaps the comment is a bit misleading. The confusion is that
>>>if you have an array declared like 'char str[10];', sizeof(str)
>>>will yield 10, whereas sizeof(str) inside PadSnprintf() will
>>>only yield the size of a pointer (4 bytes or so), regardless of
>>>the size of the array to which it points.
>>>
>>However you can apply the esoteric strlen(s) function to get the
>>length of the passed string.

>>
>What passed string?
>>
>Has it ever occurred to you to read threads before trying to
>participate in them?

>
The following was the function under discussion. If str is not a
string, it should be.

It isn't, and it shouldn't be. It is *to become* a string. What's wrong
with this buggy code that I just buggily wrote to illustrate this point?

char iamnotastring[32];
iamnotastring[0] = '\0'; /* optional - doesn't affect my point */
if(fgets(iamnot astring, strlen(iamnotas tring), stdin) != NULL)
{
...

Do try to control your love of petty objections.

You consider the distinction between a string and an array of char "petty"?

>>>>>char *PadSnprintf(ch ar *str, // the buffer

str is a pointer to the first character in a buffer that is *going to
become* a string. You can't find out how long that buffer is with strlen.
You have to be told.

And in your case, you have to be told repeatedly.

--
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

[Phil Carmody]

Re: right padding

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

You consider the distinction between a string and an array of char "petty"?

Richard, you're hereby invited to the 'Banks and the Economy'
thread which I invited to be moved here rather than continue
off-topic in alt.lang.asm. (Being about C, rather than asm,
or banks.)

Phil
--
The fact that a believer is happier than a sceptic is no more to the
point than the fact that a drunken man is happier than a sober one.
The happiness of credulity is a cheap and dangerous quality.
-- George Bernard Shaw (1856-1950), Preface to Androcles and the Lion

[Richard Heathfield]

Re: right padding

Phil Carmody said:

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

>You consider the distinction between a string and an array of char
>"petty"?

>
Richard, you're hereby invited to the 'Banks and the Economy'
thread which I invited to be moved here rather than continue
off-topic in alt.lang.asm. (Being about C, rather than asm,
or banks.)

It's kind of you, but I had a quick look and I think I'll decline, since
it's not obvious what the issue is. (I got as far as discovering that it's
about formal parameters, and someone seems to be confused about in what
contexts char [] means char [] and in what contexts it means char *.)

Why not present the issue as a simple question or statement, in a new
thread? Throwing out all the background noise will probably help
immensely.

--
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

[Phil Carmody]

Re: right padding

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

Phil Carmody said:
>

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

>>You consider the distinction between a string and an array of char
>>"petty"?

>>
>Richard, you're hereby invited to the 'Banks and the Economy'
>thread which I invited to be moved here rather than continue
>off-topic in alt.lang.asm. (Being about C, rather than asm,
>or banks.)

>
It's kind of you, but I had a quick look and I think I'll decline, since
it's not obvious what the issue is. (I got as far as discovering that it's
about formal parameters, and someone seems to be confused about in what
contexts char [] means char [] and in what contexts it means char *.)
>
Why not present the issue as a simple question or statement, in a new
thread? Throwing out all the background noise will probably help
immensely.

It appears that he's admitted he misunderstood C, so it's not just
in decline - it's over. Quite why he had to struggle and wriggle
so much on a.l.a I don't know, I thought he'd never get the point.
It appears that he misunderstood what follow-ups are too.

It's nice to know that you're here when needed though!

Cheers,
Phil
(Hi Ian!)
--
The fact that a believer is happier than a sceptic is no more to the
point than the fact that a drunken man is happier than a sober one.
The happiness of credulity is a cheap and dangerous quality.
-- George Bernard Shaw (1856-1950), Preface to Androcles and the Lion

[Ian Collins]

Re: right padding

Phil Carmody wrote:

>
Cheers,
Phil
(Hi Ian!)

G'day Phil!

--
Ian Collins