printf appends null terminator to formatted output

[acesme]

Hello,
Thank you for the fantastic work.
Should printf append a null terminator at the end of the formatted output? The standard seems to be unclear about this. The only statement I could find in the c11 standard regarding this is "The fprintf function returns when the end of the format string is encountered." [§7.21.6.1.2] (according to the standard, printf is equivalent to fprintf except for the first argument).

[mpaland]

Hello @acesme ,
thank you for your comment!
As a matter of fact, it's a really good question. I would say (or suggest) it shouldn't.
In the moment, the low level _putchar() function is responsible for the printf() output, so any \0 could be filtered out easily.
Normally the plain native printf()is used to output strings to the screen or a terminal and a terminator isn't needed or even unwanted.
Have to check it... Any other opinions/suggestions here?

[acesme]

Yes, it is simple to filter out the final '\0' in the _putchar() implementation.
It is also possible (albeit a little hacky) to fix this on 653rd row of printf.c by checking if out == _out_char and opting to not append the '\0' (or something like that).
I have no other suggestions that I can think of for now.

[mpaland]

I think, it's better to "fix" this in _out_char() itself, so other output functions won't get any penalty, something like

static inline void _out_char(char character, char* buffer, size_t idx, size_t maxlen)
{
  (void)buffer; (void)idx; (void)maxlen;
  if (character) {
    _putchar(character);
  }
}

[mpaland]

I think, suppressing the terminating \0 is conform to the standard.
@acesme, thanx for bringing this to attention. Fixed.