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

string::at

Return a character with bounds checking.

char&
at(
    std::size_t pos,
    boost::source_location const& loc = BOOST_CURRENT_LOCATION);
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char const&
at(
    std::size_t pos,
    boost::source_location const& loc = BOOST_CURRENT_LOCATION) const;
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