How to left pad a string with spaces?

[nospam]

If I have a string say:

myvar[128] = "This is a string";



How do I use sprintf to convert the string so it has 4 spaces padded on
the left like:



" This is a string";


Thanks!

[Ben Bacarisse]

Re: How to left pad a string with spaces?

nospam <no@spam.comwri tes:

If I have a string say:
>
myvar[128] = "This is a string";
>
How do I use sprintf to convert the string so it has 4 spaces padded on
the left like:
>
" This is a string";

If you mean "in place" -- the result ending up in the same array -- then
you can't do it directly because sprintf is undefined if used with
overlapping objects.

Using memmove and memset is, IMO, the simplest way to do this.

--
Ben.

[Jens Thoms Toerring]

Re: How to left pad a string with spaces?

nospam <no@spam.comwro te:

If I have a string say:

myvar[128] = "This is a string";

I guess that's supposed to be

char myvar[128] = "This is a string";

How do I use sprintf to convert the string so it has 4 spaces padded on
the left like:

" This is a string";

sprint() doesn't convert strings, it prints into a string.
It looks as if you would like to use sprintf() with 'myvar'
as both the source and the destination and that's not pos-
sible. The C standard says about this specifically:

If copying takes place between objects that overlap,
the behavior is undefined.

which exactly addresses this situation. So there's no way
you can do this reliably with sprintf().

I guess in the end you want to do something more complicated
but for what you describe you want to do a simple

memmove( myvar + 4, myvar, strlen( myvar ) + 1 );
memset( myvar, ' ', 4 );

will do. Note the use of memmove() instead of memcpy() which
is required since source and destination overlap.

Regards, Jens
--
\ Jens Thoms Toerring ___ jt@toerring.de
\______________ ____________ http://toerring.de

[nospam]

Re: How to left pad a string with spaces?

On Mon, 09 Jun 2008 23:28:17 +0000, Jens Thoms Toerring wrote:

nospam <no@spam.comwro te:

>If I have a string say:

>

>myvar[128] = "This is a string";

>
I guess that's supposed to be
>
char myvar[128] = "This is a string";
>

>How do I use sprintf to convert the string so it has 4 spaces padded on
>the left like:

>

>" This is a string";

>
sprint() doesn't convert strings, it prints into a string.
It looks as if you would like to use sprintf() with 'myvar'
as both the source and the destination and that's not pos-
sible. The C standard says about this specifically:
>
If copying takes place between objects that overlap,
the behavior is undefined.
>
which exactly addresses this situation. So there's no way
you can do this reliably with sprintf().
>
I guess in the end you want to do something more complicated
but for what you describe you want to do a simple
>
memmove( myvar + 4, myvar, strlen( myvar ) + 1 );
memset( myvar, ' ', 4 );
>
will do. Note the use of memmove() instead of memcpy() which
is required since source and destination overlap.
>
Regards, Jens

I need to use sprintf, similar to the legacy code I'm working with.
Something like this:

strncpy(fname,t mp+21,9); fname[9] = '\0';
strncpy(mname,t mp+31,1); mname[1] = '\0';

sprintf(tmp,"%4 s%-20s%-20s%-32s%-4s",
" ",fname,mname,l name," ");

[nospam]

Re: How to left pad a string with spaces?

On Tue, 10 Jun 2008 00:17:45 +0100, Ben Bacarisse wrote:

nospam <no@spam.comwri tes:
>

>If I have a string say:
>>
>myvar[128] = "This is a string";
>>
>How do I use sprintf to convert the string so it has 4 spaces padded on
>the left like:
>>
>" This is a string";

>
If you mean "in place" -- the result ending up in the same array -- then
you can't do it directly because sprintf is undefined if used with
overlapping objects.
>
Using memmove and memset is, IMO, the simplest way to do this.

I need to use sprintf, similar to the legacy code I'm working with.
Something like this:

strncpy(fname,t mp+21,9); fname[9] = '\0';
strncpy(mname,t mp+31,1); mname[1] = '\0';

sprintf(tmp,"%4 s%-20s%-20s%-32s%-4s",
" ",fname,mname,l name," ");

[CBFalconer]

Re: How to left pad a string with spaces?

nospam wrote:

>
If I have a string say:
>
myvar[128] = "This is a string";
>
How do I use sprintf to convert the string so it has 4 spaces
padded on the left like:
>
" This is a string";

For example, assuming you know s has space for the extra chars:

void sstretch(char *s, int amount) {
char *p1, *p2;

if (amount) {
pi = strchr(s, '\0');
if ((p1 s) && amount) {
p2 = p1 + amount;
do { /* move the string */
*p2-- = *p1--;
} while {p1 s);
}
while (amount) { /* inject the blanks */
*s++ = ' ';
amount--;
}
}
} /* untested */

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


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

[Ben Bacarisse]

Re: How to left pad a string with spaces?

nospam <no@spam.comwri tes:

On Tue, 10 Jun 2008 00:17:45 +0100, Ben Bacarisse wrote:
>

>nospam <no@spam.comwri tes:
>>

>>If I have a string say:
>>>
>>myvar[128] = "This is a string";
>>>
>>How do I use sprintf to convert the string so it has 4 spaces padded on
>>the left like:
>>>
>>" This is a string";

>>
>If you mean "in place" -- the result ending up in the same array -- then
>you can't do it directly because sprintf is undefined if used with
>overlapping objects.
>>
>Using memmove and memset is, IMO, the simplest way to do this.

>
>
>
I need to use sprintf, similar to the legacy code I'm working with.
Something like this:

Why do you *need* to do it any particular way? I suspect we mean
different things by "need".

strncpy(fname,t mp+21,9); fname[9] = '\0';
strncpy(mname,t mp+31,1); mname[1] = '\0';
>
sprintf(tmp,"%4 s%-20s%-20s%-32s%-4s",
" ",fname,mname,l name," ");

If you *must* use sprintf, what would constitute use of sprintf?
Would this count?

memmove(myvar + 4, myvar, strlen(myvar) + 1);
sprintf(myvar, " ");
myvar[3] = ' ';

what about:

memmove(myvar + 4, myvar, strlen(myvar) + 1);
memset(myvar, ' ', 4);
sprintf(myvar + strlen(myvar), "");

?

All of this assumes that you need it done in-place. It is just
possible that what you are asking for is:

sprintf(tmp, " %s", myvar);

but that seems so obvious as to be an unlikely question.

--
Ben.

[Ben Bacarisse]

Re: How to left pad a string with spaces?

CBFalconer <cbfalconer@yah oo.comwrites:

nospam wrote:

>>
>If I have a string say:
>>
>myvar[128] = "This is a string";
>>
>How do I use sprintf to convert the string so it has 4 spaces
>padded on the left like:
>>
>" This is a string";

>
For example, assuming you know s has space for the extra chars:
>
void sstretch(char *s, int amount) {
char *p1, *p2;
>
if (amount) {
pi = strchr(s, '\0');
if ((p1 s) && amount) {
p2 = p1 + amount;
do { /* move the string */
*p2-- = *p1--;
} while {p1 s);
}
while (amount) { /* inject the blanks */
*s++ = ' ';
amount--;
}
}
} /* untested */

Yuck. Two typos and two logic errors. You complain about not posting
corrections, so the correction is:

void sstretch(char *s, size_t amount)
{
memmove(s + amount, s, strlen(s) + 1);
memset(s, ' ', amount);
}

Why would you do all those gymnastics with the potential (so well
demonstrated) for errors?

--
Ben.

[Richard]

Re: How to left pad a string with spaces?

Ben Bacarisse <ben.usenet@bsb .me.ukwrites:

CBFalconer <cbfalconer@yah oo.comwrites:
>

>nospam wrote:

>>>
>>If I have a string say:
>>>
>>myvar[128] = "This is a string";
>>>
>>How do I use sprintf to convert the string so it has 4 spaces
>>padded on the left like:
>>>
>>" This is a string";

>>
>For example, assuming you know s has space for the extra chars:
>>
> void sstretch(char *s, int amount) {
> char *p1, *p2;
>>
> if (amount) {
> pi = strchr(s, '\0');
> if ((p1 s) && amount) {
> p2 = p1 + amount;
> do { /* move the string */
> *p2-- = *p1--;
> } while {p1 s);
> }
> while (amount) { /* inject the blanks */
> *s++ = ' ';
> amount--;
> }
> }
> } /* untested */

>
Yuck. Two typos and two logic errors. You complain about not posting
corrections, so the correction is:
>
void sstretch(char *s, size_t amount)
{
memmove(s + amount, s, strlen(s) + 1);
memset(s, ' ', amount);
}
>
Why would you do all those gymnastics with the potential (so well
demonstrated) for errors?

I would also point out to the beginner, and "Chuck", to read the man
pages and to see why memmove is better than memcpy in this and other
situations. What the hell is that horrific mess above the correct
solution?!?!

[Ben Bacarisse]

Re: How to left pad a string with spaces?

Richard<rgrdev@ gmail.comwrites :

Ben Bacarisse <ben.usenet@bsb .me.ukwrites:

<snip>

>void sstretch(char *s, size_t amount)
>{
> memmove(s + amount, s, strlen(s) + 1);
> memset(s, ' ', amount);
>}
>>

>
I would also point out to the beginner, and "Chuck", to read the man
pages and to see why memmove is better than memcpy in this and other
situations.

That is an odd way of putting it. memmove is *essential* in this
situation. In other situations memcpy may be better. I did not
explain because someone else has already done so.

--
Ben.

[Richard]

Re: How to left pad a string with spaces?

Ben Bacarisse <ben.usenet@bsb .me.ukwrites:

Richard<rgrdev@ gmail.comwrites :
>

>Ben Bacarisse <ben.usenet@bsb .me.ukwrites:

<snip>

>>void sstretch(char *s, size_t amount)
>>{
>> memmove(s + amount, s, strlen(s) + 1);
>> memset(s, ' ', amount);
>>}
>>>

>>
>I would also point out to the beginner, and "Chuck", to read the man
>pages and to see why memmove is better than memcpy in this and other
>situations.

>
That is an odd way of putting it. memmove is *essential* in this
situation. In other situations memcpy may be better. I did not
explain because someone else has already done so.

I didnt see any other post on the matter. "better" is mentioned to get
people to read the man pages. Self help and all that. I see nothing odd
at all in mentioning it as "better".

[Ben Bacarisse]

Re: How to left pad a string with spaces?

Richard<rgrdev@ gmail.comwrites :

Ben Bacarisse <ben.usenet@bsb .me.ukwrites:
>

>Richard<rgrdev @gmail.comwrite s:
>>

>>Ben Bacarisse <ben.usenet@bsb .me.ukwrites:

><snip>

>>>void sstretch(char *s, size_t amount)
>>>{
>>> memmove(s + amount, s, strlen(s) + 1);
>>> memset(s, ' ', amount);
>>>}
>>>>
>>>
>>I would also point out to the beginner, and "Chuck", to read the man
>>pages and to see why memmove is better than memcpy in this and other
>>situations.

>>
>That is an odd way of putting it. memmove is *essential* in this
>situation. In other situations memcpy may be better. I did not
>explain because someone else has already done so.

>
I didnt see any other post on the matter.

Message ID: <6b5skhF3ant6cU 1@mid.uni-berlin.de Jens Thoms Toerring:

"Note the use of memmove() instead of memcpy() which is required
since source and destination overlap."

--
Ben.

[pete]

Re: How to left pad a string with spaces?

nospam wrote:

If I have a string say:
>
myvar[128] = "This is a string";
>
>
>
How do I use sprintf to convert the string so it has 4 spaces padded on
the left like:
>
>
>
" This is a string";

/* BEGIN new.c */

#include <stdio.h>

int main(void)
{
char myvar[128] = "This is a string";

sprintf(myvar, "%20s", "This is a string");
puts(myvar);
return 0;
}

/* END new.c */

--
pete

[rahul]

Re: How to left pad a string with spaces?

On Jun 10, 7:57 am, Richard<rgr...@ gmail.comwrote:

Ben Bacarisse <ben.use...@bsb .me.ukwrites:

CBFalconer <cbfalco...@yah oo.comwrites:

>

nospam wrote:

>

>If I have a string say:

>

>myvar[128] = "This is a string";

>

>How do I use sprintf to convert the string so it has 4 spaces
>padded on the left like:

>

>" This is a string";

>

For example, assuming you know s has space for the extra chars:

>

void sstretch(char *s, int amount) {
char *p1, *p2;

>

if (amount) {
pi = strchr(s, '\0');
if ((p1 s) && amount) {
p2 = p1 + amount;
do { /* move the string */
*p2-- = *p1--;
} while {p1 s);
}
while (amount) { /* inject the blanks */
*s++ = ' ';
amount--;
}
}
} /* untested */

>

Yuck. Two typos and two logic errors. You complain about not posting
corrections, so the correction is:

>

void sstretch(char *s, size_t amount)
{
memmove(s + amount, s, strlen(s) + 1);
memset(s, ' ', amount);
}

>

Why would you do all those gymnastics with the potential (so well
demonstrated) for errors?

>
I would also point out to the beginner, and "Chuck", to read the man
pages and to see why memmove is better than memcpy in this and other
situations. What the hell is that horrific mess above the correct
solution?!?!

Other than the overlapping memory case, how is memmove supposed to be
better than memcpy?
I am unaware of any other scenario in which memmove is better than
memcpy.

[CBFalconer]

Re: How to left pad a string with spaces?

Ben Bacarisse wrote:

CBFalconer <cbfalconer@yah oo.comwrites:
>

.... snip ...

>

> void sstretch(char *s, int amount) {
> char *p1, *p2;
>>
> if (amount) {
> pi = strchr(s, '\0');
> if ((p1 s) && amount) {
> p2 = p1 + amount;
> do { /* move the string */
> *p2-- = *p1--;
> } while {p1 s);
> }
> while (amount) { /* inject the blanks */
> *s++ = ' ';
> amount--;
> }
> }
> } /* untested */

>
Yuck. Two typos and two logic errors. You complain about not posting
corrections, so the correction is:
>
void sstretch(char *s, size_t amount)
{
memmove(s + amount, s, strlen(s) + 1);
memset(s, ' ', amount);
}

One does it for the exercise. I see only one typo [while {p1 >
s)]] and one unnecessary test [&& amount]. A compilation may well
show up more. What did you see?

Incidentally, a speed comparison would be interesting. I don't
think your version allows for amount == 0 and for an empty original
string. I would have to check the specs for memove and memset with
care.

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


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