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POstringstream unsigned input validation
 

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    <p>I'm writing part of program which parses and validates some user input in program console arguments. I choose to use stringstream for that purpose, but encounter a problem with unsigned types reading.</p> <p>Next template is intended for reading requested type from given string:</p> <pre><code>#include &lt;iostream&gt; #include &lt;sstream&gt; #include &lt;string&gt; using std::string; using std::stringstream; using std::cout; using std::endl; template&lt;typename ValueType&gt; ValueType read_value(string s) { stringstream ss(s); ValueType res; ss &gt;&gt; res; if (ss.fail() or not ss.eof()) throw string("Bad argument: ") + s; return res; } // +template specializations for strings, etc. int main(void) { cout &lt;&lt; read_value&lt;unsigned int&gt;("-10") &lt;&lt; endl; } </code></pre> <p>In case type is unsigned and input string contains negative number I expect to see exception throw (caused by <code>ss.fail() = true</code>). But stringstream produces casted to unsigned type value (4294967286 in written sample).</p> <p>How can be this sample fixed to achieve desired behavior (preferable without fallback to c functions)? I understand that it can be done with simple first symbol check but I can put leading spaces for example. I can write own parser but don't believe that problem is so unpredictable and standard library unable to solve it.</p> <p>Functions hidden in deep of stringstream operators for unsigned types are strtoull and strtoul. They work in described manner but <em>mentioned functions are low-level</em>. Why stringstream do not provide some validation level? (I just hope I'm wrong and it does but some movements required to enable this).</p>
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    1. COI saw this thread but there was a problem with inconsistent behavior in different compilers. And finally behavior on MS VS and modern GCC was just convert to unsigned representation as far as I understood.
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