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]

nospam <[e-mail] 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]

nospam <[e-mail] 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 ___ [e-mail]
\______________ ____________ http://toerring.de

[nospam]

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

nospam <[e-mail] 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]

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

nospam <[e-mail] 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]

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]

nospam <[e-mail] tes:

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

>nospam <[e-mail] 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]

CBFalconer <cb********@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]

Ben Bacarisse <be********@bsb .me.ukwrites:

CBFalconer <cb********@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?!?!

[rahul]

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.