[FFmpeg-devel] [PATCH 1/3] avformat/avio: add avio_print_n_strings and avio_print

[Marton Balint]

On Sun, 11 Aug 2019, Reimar Döffinger wrote:

> On 11.08.2019, at 20:41, Reimar Döffinger <Reimar.Doeffinger at gmx.de> wrote:
>
>> On 05.08.2019, at 23:34, Marton Balint <cus at passwd.hu> wrote:
>> 
>>> These functions can be used to print a variable number of strings consecutively
>>> to the IO context. Unlike av_bprintf, no temporery buffer is necessary.
>> 
>> Hm, is there a use-example patch I missed?
>
> Sorry, I see it now, and also the argument about the macro providing type checking.
> Ignore me if you feel the code is fine as-is.
>
>> Also is the #define ugliness worth it compared to just requiring NULL termination?
>> You can use the sentinel function attribute to have the compiler check that users do not forget it.

There is yet another approach which does not count parameters but uses a 
NULL sentinel, and is more simple:

void avio_print_string_array(AVIOContext *s, const char *strings[])
{
     for(; strings[0]; strings++)
         avio_write(s, (const unsigned char *)strings[0], strlen(strings[0]));
}

#define avio_print(s, ...) \
     avio_print_string_array(s, (const char*[]){__VA_ARGS__, NULL})

This might also has the benefit that __VA_ARGS__ is referenced only once, 
because for the old version some compilers (msvc) was not optimizing away 
the additional local variable and their string references which were used 
in the sizeof magic.

I can change the patch to use this version if people prefer.

Regards,
Marton