va_list passthrough

[raphfrk]

Is there any way to pass a variable list to a function, so as to act
as a passthrough?

for example:

void new_printf ( char *buf , ... )
{
va_list vlist;

<modify buf slightly>

printf( buf , vlist );
}

[santosh]

raphfrk wrote:

Is there any way to pass a variable list to a function, so as to act
as a passthrough?

for example:

void new_printf ( char *buf , ... )
{
va_list vlist;

<modify buf slightly>

printf( buf , vlist );
}

Use va_copy.

[raphfrk]

On Jul 7, 11:03 am, santosh <santosh....@gm ail.comwrote:

raphfrk wrote:

Is there any way to pass a variable list to a function, so as to act
as a passthrough?

for example:

void new_printf ( char *buf , ... )
{
va_list vlist;

<modify buf slightly>

printf( buf , vlist );
}

Use va_copy.

I don't think that is what I want.

I want a program that would allow something like the following to
work.

#include <stdio.h>

int main()
{

int a=7l;

new_printf("%d\ n" , a );

return 0;
}

void new_printf ( char *buf , ... )
{

printf( buf , ... ); // the va list is passed to printf

}

The effect of the above would be that new_printf acts the same as
printf.

[rahul]

On Jul 7, 3:01*pm, raphfrk <raph...@netsca pe.netwrote:

Is there any way to pass a variable list to a function, so as to act
as a passthrough?

for example:

void new_printf ( char *buf , ... )
{
* va_list vlist;

* <modify buf slightly>

* printf( buf , vlist );

}

Use va_copy.
#include <stdarg.h>
void va_copy(va_list dest, va_list src);

The prototype is self explanatory. How do you plan to modify va_list?

[raphfrk]

On Jul 7, 11:59 am, rahul <rahulsin...@gm ail.comwrote:

On Jul 7, 3:01 pm, raphfrk <raph...@netsca pe.netwrote:

Is there any way to pass a variable list to a function, so as to act
as a passthrough?

for example:

void new_printf ( char *buf , ... )
{
va_list vlist;

<modify buf slightly>

printf( buf , vlist );

}

Use va_copy.
#include <stdarg.h>
void va_copy(va_list dest, va_list src);

The prototype is self explanatory. How do you plan to modify va_list?

I don't, I want to pass the va_list to the printf function (any
modifications would be to the buf field).

[Kenny McCormack]

In article <62************ *************** *******@j22g200 0hsf.googlegrou ps.com>,
raphfrk <ra*****@netsca pe.netwrote:
....

>Use va_copy.
#include <stdarg.h>
void va_copy(va_list dest, va_list src);

The prototype is self explanatory. How do you plan to modify va_list?

I don't, I want to pass the va_list to the printf function (any
modification s would be to the buf field).

For some reason, nobody here wants to tell you about the vprintf() function.

This is in line with official, stated, CLC policy - which is to never
give a sucker an even break.

[Ben Bacarisse]

raphfrk <ra*****@netsca pe.netwrites:

On Jul 7, 11:03 am, santosh <santosh....@gm ail.comwrote:

>raphfrk wrote:

Is there any way to pass a variable list to a function, so as to act
as a passthrough?

Only if it accepts a va_list.

for example:

void new_printf ( char *buf , ... )
{
va_list vlist;

<modify buf slightly>

printf( buf , vlist );
}

Use va_copy.

I don't think that is what I want.

I want a program that would allow something like the following to
work.

#include <stdio.h>

int main()
{

int a=7l;

new_printf("%d\ n" , a );

return 0;
}

void new_printf ( char *buf , ... )
{

printf( buf , ... ); // the va list is passed to printf

}

The effect of the above would be that new_printf acts the same as
printf.

Thare are v* versions of the printf family of function for this
purpose. You want vprintf.

--
Ben.

[raphfrk]

On Jul 7, 12:21 pm, gaze...@xmissio n.xmission.com (Kenny McCormack)
wrote:

In article <623e246f-f0ff-4bbf-a334-a9bb5aecf...@j2 2g2000hsf.googl egroups.com>,ra phfrk <raph...@netsca pe.netwrote:

...

Use va_copy.
#include <stdarg.h>
void va_copy(va_list dest, va_list src);

The prototype is self explanatory. How do you plan to modify va_list?

I don't, I want to pass the va_list to the printf function (any
modifications would be to the buf field).

For some reason, nobody here wants to tell you about the vprintf() function.

Thanks. I guess I can assume from the existance of vprintf, that
there is no way to pass a va_list directly to printf itself ?

This is in line with official, stated, CLC policy - which is to never
give a sucker an even break.

Generally, they will correct every error in your code, including those
unrelated to the original question. However, they usually do also
answer the question too (and the list of errors can be helpful too).

[pete]

raphfrk wrote:

Thanks. I guess I can assume from the existance of vprintf, that
there is no way to pass a va_list directly to printf itself ?

That's not so bad if you realize if you realize that
printf may use, and frequently does use, vfprintf,
either directly or through vprintf.

int printf(const char *format, ...)
{
int count;
va_list arg;

va_start(arg, format);
count = vprintf(format, arg);
va_end(arg);
return count;
}

int vprintf(const char *format, va_list arg)
{
return vfprintf(stdout , format, arg);
}

I have a toy library.
http://www.mindspring.com/~pfilandr/C/library/std_io.c

--
pete

[Kenny McCormack]

In article <c7************ *************** *******@m44g200 0hsc.googlegrou ps.com>,
raphfrk <ra*****@netsca pe.netwrote:

>On Jul 7, 12:21 pm, gaze...@xmissio n.xmission.com (Kenny McCormack)
wrote:

>In article

<623e246f-f0ff-4bbf-a334-a9bb5aecf...@j2 2g2000hsf.googl egroups.com>,ra phfrk
<raph...@netsc ape.netwrote:

>>
...

>Use va_copy.
#include <stdarg.h>
void va_copy(va_list dest, va_list src);

>The prototype is self explanatory. How do you plan to modify va_list?

>I don't, I want to pass the va_list to the printf function (any
modification s would be to the buf field).

For some reason, nobody here wants to tell you about the vprintf() function.

Thanks. I guess I can assume from the existance of vprintf, that
there is no way to pass a va_list directly to printf itself ?

Correct. What this means is that every variable-number-of-args function
that exists must have a corresponding v...() version. Luckily, there
aren't very many (off the top of my head, I can only think of the printf
and scanf families) that "come with the system". But it also means that
any that you write yourself, you should also provide a v...() version of.

Which, IMHO, makes the whole va_args functionality rather useless. I
think it mainly exists for backwards compatibility with the existing
printf and scanf families.

>This is in line with official, stated, CLC policy - which is to never
give a sucker an even break.

Generally, they will correct every error in your code, including those
unrelated to the original question.

Human compilers, as they say. And about as useful. If I want a
compiler, I know where to find them.

>However, they usually do also answer the question too (and the list of
errors can be helpful too).

My experience has been otherwise. Note that I am not talking about my
own issues - i.e., I'm not whining about them not answering my questions;
I have long since realized that looking for help here is like looking in
the sewer. I'm talking about my observations of years and years of them
joyously smackin' the newbies given any opportunity.

You may, of course, have another opinion. Fantasies die hard.