Which standard C++ features can be used for querying machine/OS architecture?

Question

What are the standard C++ features and utilities for querying the properties of the hardware or operating system capabilities, on which the program is running?
For instance,

Answer 1

As others have pointed out, functions for obtaining such properties of the system are typically platform-specific. The STL and boost do not provide platform-independent wrappers, so you'll have to rely on other third party libraries.

I've successfully used SIGAR in the past:

The Sigar API provides a portable interface for gathering system information such as:

• System memory, swap, cpu, load average, uptime, logins
• Per-process memory, cpu, credential info, state, arguments, environment, open files
• File system detection and metrics
• Network interface detection, configuration info and metrics
• TCP and UDP connection tables
• Network route table

As a side note, Boost Filesystem does actually provide boost::filesystem::space to query "how much disk space is available to write to in a certain directory".