Programmatically find the number of cores on a machine

Question

Is there a way to determine how many cores a machine has from C/C++ in a platform-independent way? If no such thing exists, what about determining it per-platform (Windows/*

Answer 1

Unrelated to C++, but on Linux I usually do:

grep processor /proc/cpuinfo | wc -l

Handy for scripting languages like bash/perl/python/ruby.