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

Return a pointer to an element, or nullptr if the index is invalid.

value const*
if_contains(
    std::size_t pos) const noexcept;
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value*
if_contains(
    std::size_t pos) noexcept;
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