libc: implement scanf()

[ycsin]

This was originally added as a ticket under POSIX, but scanf() is not a POSIX function. It is from C89.

https://en.cppreference.com/w/c/io/scanf

The expectation from the POSIX API is that this function is implemented as part of whatever C library is in use.

[CiaranRoche1]

Hi, just wondering if there has been any progress made on any of these libc functions, or am I all good to try to implement some of these myself?

[cfriedt]

Hi, just wondering if there has been any progress made on any of these libc functions, or am I all good to try to implement some of these myself?

@CiaranRoche1 - I think the minimal libc might need an implementation.

Ideally, we would have an abstraction that could be used by both libc and POSIX as part of ZVFS. There are likely some hooks for picolibc and newlib that are involved. Minimal libc might need a bit more.

@ycsin - was there some progress on unlocked file I/o?

[CiaranRoche1]

@cfriedt - This sounds interesting! Right now I am looking for something to tackle as my first issue, so I might take a crack at implementing a new function in libc.

However, I would love to be involved in any progress you want to make on making an abstraction for libc and POSIX. Keep me posted!

[cfriedt]

@CiaranRoche1 - alternatively, for your first issue, it might be good to find an easy bug to tackle at the url below. Unfortunately, the good first issue label is not used very consistently in Zephyr

https://github.com/zephyrproject-rtos/zephyr/issues?q=is%3Aopen+is%3Aissue+label%3Abug