Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Access an element, with bounds checking.

value&
at(
    std::size_t pos);
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value&&
at(
    std::size_t pos);
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value const&
at(
    std::size_t pos) const;
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