So there was no extension of the functionality over time, all the formats have been supported from day one?
The key features that is used here is the '%n' format specifier, that fetches a pointer as the next argument, and writes a character count back.
There is actually an interesting question here: was '%n' always in printf, or was it added at one point?
I took a cursory look at some old Unix source archives at TUHS: https://www.tuhs.org/cgi-bin/utree.pl
As far as I can tell from the PDP-11 assembly, Version 7 research Unix (relevant file: /usr/src/libc/stdio/doprnt.s) does not appear to implement it.
The 4.1BSD version of that file even explicitly throws an error, treating it as an invalid format specifier.
The implementation in a System III archive looks suspiciously similar to the BSD one, also throwing an error.
Only in a System V R4 archive (relevant file: svr4/ucblib/libc/port/stdio/doprnt.c) I found an implementation of "%n" that works as expected.
I guess it was added at some point to System V and through that eventually made it into POSIX?
alt Hacker News
The key features that is used here is the '%n' format specifier, that fetches a pointer as the next argument, and writes a character count back.
There is actually an interesting question here: was '%n' always in printf, or was it added at one point?
I took a cursory look at some old Unix source archives at TUHS: https://www.tuhs.org/cgi-bin/utree.pl
As far as I can tell from the PDP-11 assembly, Version 7 research Unix (relevant file: /usr/src/libc/stdio/doprnt.s) does not appear to implement it.
The 4.1BSD version of that file even explicitly throws an error, treating it as an invalid format specifier.
The implementation in a System III archive looks suspiciously similar to the BSD one, also throwing an error.
Only in a System V R4 archive (relevant file: svr4/ucblib/libc/port/stdio/doprnt.c) I found an implementation of "%n" that works as expected.
I guess it was added at some point to System V and through that eventually made it into POSIX?