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    <p>Another version...</p> <p>Use <a href="http://en.cppreference.com/w/cpp/string/byte/strtol" rel="noreferrer"><code>strtol</code></a>, wrapping it inside a simple function to hide its complexity :</p> <pre><code>inline bool isInteger(const std::string &amp; s) { if(s.empty() || ((!isdigit(s[0])) &amp;&amp; (s[0] != '-') &amp;&amp; (s[0] != '+'))) return false ; char * p ; strtol(s.c_str(), &amp;p, 10) ; return (*p == 0) ; } </code></pre> <h3>Why <code>strtol</code> ?</h3> <p>As far as I love C++, sometimes the C API is the best answer as far as I am concerned:</p> <ul> <li>using exceptions is overkill for a test that is authorized to fail</li> <li>the temporary stream object creation by the lexical cast is overkill and over-inefficient when the C standard library has a little known dedicated function that does the job.</li> </ul> <h3>How does it work ?</h3> <p><code>strtol</code> seems quite raw at first glance, so an explanation will make the code simpler to read :</p> <p><code>strtol</code> will parse the string, stopping at the first character that cannot be considered part of an integer. If you provide <code>p</code> (as I did above), it sets <code>p</code> right at this first non-integer character.</p> <p>My reasoning is that if <code>p</code> is not set to the end of the string (the 0 character), then there is a non-integer character in the string <code>s</code>, meaning <code>s</code> is not a correct integer. </p> <p>The first tests are there to eliminate corner cases (leading spaces, empty string, etc.).</p> <p>This function should be, of course, customized to your needs (are leading spaces an error? etc.).</p> <h3>Sources :</h3> <p>See the description of <code>strtol</code> at: <a href="http://en.cppreference.com/w/cpp/string/byte/strtol" rel="noreferrer">http://en.cppreference.com/w/cpp/string/byte/strtol</a>.</p> <p>See, too, the description of <code>strtol</code>'s sister functions (<code>strtod</code>, <code>strtoul</code>, etc.).</p>
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    1. POHow do I check if a C++ string is an int?
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    1. CO+1, by far the best answer. lexical_cast is overkill and it borders on bad practice.
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      1. USDavid Titarenco
    2. CO@David Titarenco : `lexical_cast is overkill and it borders on bad practice` : Only when used carelessly, and the same can be said for any other feature. The real use of boost::lexical_cast is for generic code, or quick and dirty code. **Generic code:** When you have an unknown type T, using a switch to use strtol, strtol, etc. is a mistake. Using a boost::lexical_cast is the right thing, providing the boost::lexical_cast specializations for the right types for efficient use. **Quick'n'dirty code:** If that code does not need speed, then using boost::lexical_cast is the easiest way to do it.
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