Arduino IDE missing avrlibc functions?

The extended reference page on indicates that it links against avrlibc, and that any of it's functions can be used.

However, I'm finding that the IDE doesn't recognize at least one function, and that I get a function not declared error when I try to compile

j = rint(i);

error: 'rint' was not declared in this scope

Where the avrlibc docs clearly indicate the presence of the function.

I cannot seem to find a single reference for it.

I found lrint inside math.h but not rint.

Where do you find a reference for it, and what do you want to do?

Try using round() instead of rint(). It should act the same.