I agree with the advice to read your standard library, because I think there's huge value to your general understanding of lower-level concepts and to knowing the available functionality of your language, but I disagree that it is the best example of idiomatic code, necessarily. For example, C++'s STL was written to be portable, efficient, and general beyond all other goals. Modern C++ style and abstractions are nowhere to be found, and if you follow the STL style, you may over-abstract (templatize), use manual memory management, and architect for non-relevant circumstances.