questions to register_printf_specifier()

questions to register_printf_specifier()

[Walter Harms]

hi list,
i was playing with register_printf_specifier(). the documentation is sparse,
so i need some help:

I have a working example for a two argument specifier.
(looks like printf("%w\n",arg1,arg2); )

register_printf_specifier('w',usr_printf,usr_arg);

the arginfo function looks like this (reduced version).

int usr_arg (const struct printf_info *info,
             size_t n, int *argtypes,
             int *size)
{
       argtypes[n-1] = PA_STRING;

        *size=2;  // size of user-defined type ?
        return 2; //return the number of need arguments
}

the comment in printf.h say i should fill argtypes. I figured out that n
is the pos in argtypes i have to fill. Begs the questions:

What is the use of *size ? it seems i can set it to any value without any effect.

note: i am not a list member, please always CC

re,
 wh

Re: questions to register_printf_specifier()

[Florian Weimer]

* Walter Harms via Libc-alpha:

> What is the use of *size ? it seems i can set it to any value without
> any effect.

It is the size of the storage needed by the user-defined va_arg
function, registered with register_printf_type.  See
stdio-common/tst-vfprintf-user-type.c for an example.

Thanks,
Florian

AW: questions to register_printf_specifier()

[Walter Harms]

i will test it.

CU 
________________________________________
Von: Florian Weimer <fweimer@redhat.com>
Gesendet: Montag, 8. März 2021 09:05
An: Walter Harms via Libc-alpha
Cc: Walter Harms
Betreff: Re: questions to register_printf_specifier()

* Walter Harms via Libc-alpha:

> What is the use of *size ? it seems i can set it to any value without
> any effect.

It is the size of the storage needed by the user-defined va_arg
function, registered with register_printf_type.  See
stdio-common/tst-vfprintf-user-type.c for an example.

Thanks,
Florian