From my installation, a grep through the headers folder shows no remainder functions. It's possible I'm missing something, but it looks like it doesn't exist at all in the vxWorks API.
As for the extern "C" option, yes that will make it compile, however the function will most likely not be resolved by the linker, which will cause problems when you try to run it. Wind River's system is designed to not complain about missing symbols until the cRIO's kernel tries to load the program. I'll check if this is the case tomorrow.
EDIT: actually, drem() does exist, and is defined to be the same as remainder() (see
the glibc manual). However, the definition for it is in <private/trigP.h>, which isn't meant for inclusion by user programs. There don't seem to be any public headers which include it either.
__________________
"To have no errors would be life without meaning. No strugle, no joy"
"A network is only as strong as it's weakest linksys"