Hello
I want to write function which will return me string
formatted by sprintf:

char* sprintf_container(const char *format,...){
str=malloc('what size' ??);
sprintf(str,format,???);
return str;
}

But how should i pass other parameters to sprintf ?

Thanx
Michal

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vertigo <none@microsoft.com> writes:

> Hello
> I want to write function which will return me string
> formatted by sprintf:
>
> char* sprintf_container(const char *format,...){
> 	str=malloc('what size' ??);
> 	sprintf(str,format,???);
> 	return str;
> }
>
> But how should i pass other parameters to sprintf ?

man vsprintf

--
Måns Rullgård
mru@mru.ath.cx

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vertigo <none@microsoft.com> writes:

> Hello
> I want to write function which will return me string
> formatted by sprintf:
>
> char* sprintf_container(const char *format,...){
> 	str=malloc('what size' ??);
> 	sprintf(str,format,???);
> 	return str;
> }
>
> But how should i pass other parameters to sprintf ?

You won't be using sprintf.

You should really, as always, read the manual page for sprintf: man sprintf

Where you'll notice vsnprintf.
Then you'll refer to the stdarg man page: man stdarg


--
__Pascal Bourguignon__                     http://www.informatimago.com/

Our enemies are innovative and resourceful, and so are we. They never
stop thinking about new ways to harm our country and our people, and
neither do we.

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vertigo <none@microsoft.com> wrote:
> I want to write function which will return me string
> formatted by sprintf:

> char* sprintf_container(const char *format,...){
> 	str=malloc('what size' ??);
> 	sprintf(str,format,???);
> 	return str;
> }

Here's what I use for that:

#define SPRINTF_CONTAINER_TRY_LENGTH 128

char *sprintf_container( const char *fmt, ... )
{
char *c = NULL, *new_c;
size_t len = SPRINTF_CONTAINER_TRY_LENGTH;
va_list ap;
int wr;


while ( 1 )
{
if ( ( new_c = realloc( c, len ) ) == NULL )
{
free( c );
return NULL;
}
c = new_c;

va_start( ap, fmt );
wr = vsnprintf( c, len, fmt, ap );
va_end( ap );

if ( wr < 0 )         /* indicates not enough space with older glibc */
{
len *= 2;
continue;
}

if ( ( size_t ) wr + 1 > len )   /* new glibc returns the number of */
{                                /* chars needed, not counting the */
len = wr + 1;                /* trailing '\0' */
continue;
}

break;
}

/* Trim the string to the number of required characters */

if ( ( size_t ) wr + 1 < len )
{
if ( ( new_c = realloc( c, ( size_t ) wr + 1 ) ) == NULL )
return c;
else
c = new_c;
}

return c;
}

Regards, Jens
--
\   Jens Thoms Toerring  ___  Jens.Toerring@physik.fu-berlin.de
\__________________________  http://www.toerring.de

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On Fri, 27 Aug 2004 11:48:53 +0200
vertigo <none@microsoft.com> wrote:

> Hello
> I want to write function which will return me string
> formatted by sprintf:
>
> char* sprintf_container(const char *format,...){
> 	str=malloc('what size' ??);
> 	sprintf(str,format,???);
> 	return str;
> }
>
> But how should i pass other parameters to sprintf ?
>
> Thanx
> Michal
>

or you could use asprintf().  not standard C, but it is portable on linux an
d
bsd.

--
-sean

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Jens.Toerring@physik.fu-berlin.de wrote:
> vertigo <none@microsoft.com> wrote:
> 
>
> 
>
>
> Here's what I use for that:
>
> #define SPRINTF_CONTAINER_TRY_LENGTH 128
>
> char *sprintf_container( const char *fmt, ... )
> {
>     char *c = NULL, *new_c;
>     size_t len = SPRINTF_CONTAINER_TRY_LENGTH;
>     va_list ap;
>     int wr;
>
>
>     while ( 1 )
>     {
>         if ( ( new_c = realloc( c, len ) ) == NULL )
>         {
>             free( c );

if realloc() fails, your program will crash on most free() implementations.



--
Lev Walkin
vlm@lionet.info

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Lev Walkin <vlm@lionet.info> wrote:[vbcol=seagreen]
> Jens.Toerring@physik.fu-berlin.de wrote: 
[vbcol=seagreen]
> if realloc() fails, your program will crash on most free() implementations.[/vbcol
]

In that case 'c' should be either a value returned from a previous call
of alloc(), in which case I don't see a problem, or NULL, and then it
should be a no-op (as far as I can see from the C89 standard). Or am I
overlooking something?
Regards, Jens
--
\   Jens Thoms Toerring  ___  Jens.Toerring@physik.fu-berlin.de
\__________________________  http://www.toerring.de

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Jens.Toerring@physik.fu-berlin.de wrote:
> Lev Walkin <vlm@lionet.info> wrote:
> 
>
> 
>
>
> In that case 'c' should be either a value returned from a previous call
> of alloc(), in which case I don't see a problem, or NULL, and then it
> should be a no-op (as far as I can see from the C89 standard). Or am I
> overlooking something?

you're overlooking the real world.

however, I've just checked, and indeed it seem to have improved on newer
systems. however, I remember this being a common inconvenience on the older
ones, so it's better not to rely on it.


--
Lev Walkin
vlm@lionet.info

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William Ahern wrote:
> Lev Walkin <vlm@lionet.info> wrote:
> 
>
>
> Care to elaborate? I'm quite surprised to hear that.

The code checks for old behavior of vsnprintf(), which may return -1 instead
of the "estimated" numer of characters. But the code does not go further and
check if the c is non-0 before free()'ing. See my other follow-up on the C89
quote.


--
Lev Walkin
vlm@lionet.info

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Lev Walkin <vlm@lionet.info> wrote:
> William Ahern wrote: 
[vbcol=seagreen]
> The code checks for old behavior of vsnprintf(), which may return -1 inste
ad
> of the "estimated" numer of characters. But the code does not go further a
nd
> check if the c is non-0 before free()'ing. See my other follow-up on the C
89
> quote.

Luckily, I don't remember having to deal with a C version that didn't
work correctly with free() on NULL (but fortunately one tends to forget
about such annoyances and normally, i.e. in the code I really use, I
avoid it anyway because I usually would take it to be an indication
that something went wrong when free() is called with a NULL pointer).
But vsnprintf() is a different case because it's in C99 only, so one
can't reasonably expect that all implementations got it already right
(if they have it at all), so additional checks are (still) in order.
Perhaps I sshould have made it more clear that the code I posted only
works with a system that conforms to C89 and has a vsnprintf() imple-
mentation that either is C99 conformant or returns a negative value
when the the length of the buffer is insufficient.

Regards, Jens
--
\   Jens Thoms Toerring  ___  Jens.Toerring@physik.fu-berlin.de
\__________________________  http://www.toerring.de

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