Does general purpose libraries contain any code which cannot be written by normal users?

Do libraries such as boost, STL, ACE (which often make inclusions in namespace std) contain any special kind of coding techniques which is not possible to be coded/used by a usual programmer ?

In a broader sense, do they leverage any compiler or implementation specific utilities, which is not 开发者_如何学Cexposed to the general programmers ?

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These are all written in the same code available to everyone. However, the code is often hard to read (at least for me) because they go to great lengths to ensure the generality of the libraries. Here is the sgi implementation of the STL. Browse through it and see for yourself.

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Since the standard library is part of the C++ specification, your question is not well-founded.

For example, the implementation of std::fstream (or at least, std::filebuf) must use OS-dependent interfaces. Do those count as "implementation specific utilities"?

The bottom line is that the spec does not separate out the standard library from the rest of the language. It is all just part of the language, and its facilities are available to "usual programmers".

Boost is mostly written in standard C++, but they do take advantage of platform-specific features when that can yield performance improvements, and they occasionally need compiler-dependent extensions for features. The documentation will generally mention when a feature is not available on all platforms.

I do not know about ACE.

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The STL (and the others) is written in 'pure C++'. See here for a very similar question.

C, on the other hand, has many system calls (unix/Windows/etc) in its standard library files to make everything work.

The C++0x STL also uses some compiler magic to make some new language features work.