What does ap in printf(3) stand for?

What does ap in printf(3) stand for?

[Peng Yu]

https://man7.org/linux/man-pages/man3/printf.3.html

It is not clear what "ap" stands for in printf(3). Could anybody
explain what it stands for? Thanks.

-- 
Regards,
Peng

Re: What does ap in printf(3) stand for?

[tomas]

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On Tue, May 11, 2021 at 11:50:20AM -0500, Peng Yu via Libc-help wrote:
> https://man7.org/linux/man-pages/man3/printf.3.html
> 
> It is not clear what "ap" stands for in printf(3). Could anybody
> explain what it stands for? Thanks.

This is for the v*printf group. The ap is a va_list in the sense of
stdarg. Let me quote the man page:

  "The functions vprintf(), vfprintf(), vdprintf(), vsprintf(),
   vsnprintf() are equivalent to the functions printf(),
   fprintf(), dprintf(), sprintf(), snprintf(), respectively,
   except that  they  are called  with a va_list instead of a
   variable number of arguments.  These functions do not call
   the va_end macro.  Because they invoke the va_arg macro,
   the value of ap is undefined after the call.  See stdarg(3)."

They are typically used if you want to somehow leverage or extend
printf: you unwrap the parameters "the stdarg way" and pass on
whatever is left to v*printf.

Cheers
 - t

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Re: What does ap in printf(3) stand for?

[Peng Yu]

You misunderstood my question. I literally mean what the two letters
"a" and "p" stand for respectively.

Just like "E", "O" and "F" in "EOF" stand for "end", "of" and "file",
respectively.

My guess is "a" stands for "argument", but then it should be a list.
Thus it should be called "al" instead of "ap". So I don't understand
what "p" stands for.

On 5/11/21, tomas@tuxteam.de <tomas@tuxteam.de> wrote:
> On Tue, May 11, 2021 at 11:50:20AM -0500, Peng Yu via Libc-help wrote:
>> https://man7.org/linux/man-pages/man3/printf.3.html
>>
>> It is not clear what "ap" stands for in printf(3). Could anybody
>> explain what it stands for? Thanks.
>
> This is for the v*printf group. The ap is a va_list in the sense of
> stdarg. Let me quote the man page:
>
>   "The functions vprintf(), vfprintf(), vdprintf(), vsprintf(),
>    vsnprintf() are equivalent to the functions printf(),
>    fprintf(), dprintf(), sprintf(), snprintf(), respectively,
>    except that  they  are called  with a va_list instead of a
>    variable number of arguments.  These functions do not call
>    the va_end macro.  Because they invoke the va_arg macro,
>    the value of ap is undefined after the call.  See stdarg(3)."
>
> They are typically used if you want to somehow leverage or extend
> printf: you unwrap the parameters "the stdarg way" and pass on
> whatever is left to v*printf.
>
> Cheers
>  - t
>


-- 
Regards,
Peng

Re: What does ap in printf(3) stand for?

[Sergey Organov]

Peng Yu via Libc-help
<libc-help@sourceware.org> writes:

> https://man7.org/linux/man-pages/man3/printf.3.html
>
> It is not clear what "ap" stands for in printf(3). Could anybody
> explain what it stands for? Thanks.

ap == argument pointer:

https://stackoverflow.com/questions/24345199/what-does-ap-stand-for-in-c-examples

-- Sergey Organov