Add fgets to File Impl in FS.h

[mjs513]

Ran across an issue that fgets was not supported. Looking through the forum seems like a few other people ok maybe one or two. But it also looks like a handy function to have available so added it. You can look here for a quick test: https://forum.pjrc.com/index.php?threads/problems-with-external-library-using-sdfat.77492/post-363551

Will make a similar change to the SD library.

[A-Dunstan]

This is not something that should be implemented in the File/FS classes, the real (libc) fgets function is usable by properly implementing _read() and _write() to use File objects as int file descriptors (fds).

(This is also a bad implementation - doesn't check if f is valid before calling the fgets virtual method on it.)

[mjs513]

@PaulStoffregen
Just for reference fgets is implemented in the SdFat library, e.g.,

also for ref
https://github.com/search?q=repo%3Agreiman%2FSdFat%20fgets&type=code

Here is the example from sdfat: https://github.com/greiman/SdFat/blob/cda057318bec196183d4cc92b01bc1dd64bbfb02/examples/examplesV1/fgets/fgets.ino#L16

And here is a link I posted: https://forum.pjrc.com/index.php?threads/file-abstraction-and-sdfat-integration.64136/

Of course Paul its your call.

[mjs513]

Based on a suggestion by @KurtE changed the virtual fgets function call from

virtual int fgets(char* str, int num, char* delim = nullptr) = 0;

to

virtual int fgets(char* str, int num, char* delim = nullptr){ return -1; }

should

Then if littlefs or my dummy classes should rebuild and run with out changes

[ssilverman]

I’m with @A-Dunstan on this one. I don’t think this belongs in File either.