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copied!<p>Unfortunately I don't have enough rep yet to comment...</p> <p><code>lexical_cast</code> is not primarily slow because it's generic (template lookups happen at compile-time, so virtual function calls or other lookups/dereferences aren't necessary). <code>lexical_cast</code> is, in my opinion, slow, because it builds on C++ iostreams, which are primarily intended for streaming operations and not single conversions, and because <code>lexical_cast</code> must check for and convert iostream error signals. Thus:</p> <ul> <li>a stream object has to be created and destroyed</li> <li>in the string output case above, note that C++ compilers have a hard time avoiding buffer copies (an alternative is to format directly to the output buffer, like <code>sprintf</code> does, though <code>sprintf</code> won't safely handle buffer overruns)</li> <li><code>lexical_cast</code> has to check for <code>stringstream</code> errors (<code>ss.fail()</code>) in order to throw exceptions on conversion failures</li> </ul> <p><code>lexical_cast</code> is nice because (IMO) exceptions allow trapping all errors without extra effort and because it has a uniform prototype. I don't personally see why either of these properties necessitate slow operation (when no conversion errors occur), though I don't know of such C++ functions which are fast (possibly Spirit or boost::xpressive?).</p> <p>Edit: I just found a message mentioning the use of <code>BOOST_LEXICAL_CAST_ASSUME_C_LOCALE</code> to enable an "itoa" optimisation: <a href="http://old.nabble.com/lexical_cast-optimization-td20817583.html" rel="noreferrer">http://old.nabble.com/lexical_cast-optimization-td20817583.html</a>. There's also a linked <a href="http://accu.org/index.php/journals/1375#Boost" rel="noreferrer">article</a> with a bit more detail.</p>

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