You use your own or someone else's non-standard wrapper libraries for specific OS services. For instance if you want to do asynchronous IO, or use virtual memor

You use your own or someone else's non-standard wrapper libraries for specific OS services. For instance if you want to do asynchronous IO, or use virtual memory features, the C standard library is entirely useless anyway, so you create your own thin cross-platform wrappers over OS specific system API calls, or even call those OS specific functions directly (e.g. POSIX functions on UNIX-flavoured operating systems or Win32 functions on Windows). The C stdlib is essentially an SDK for very simple 70's UNIX-style command line tools, but operating systems have moved on, while the C standard library is unfortunately stuck in the past. (IMHO a "C stdlib v2" would be much more important than any new language features, but it doesn't look like the C committee wants to go down that road).