[29.9] What is the "standard library"? What is included / excluded from it?
Most (not all) implementations have a "standard include" directory, sometimes
directories plural. If your implementation is like that, the headers in the
standard library are probably a subset of the files in those directories. For
example, iostream and string are part of the standard library,
as is cstring and cstdio. There are a bunch of .h files that
are also part of the standard library, but not every .h file in those
directories is part of the standard library. For example, stdio.h is
but windows.h is not.
You include headers from the standard library like this:
#include <iostream>
int main()
{
std::cout << "Hello world!\n";
...
}