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POIs it possible to read infinity or NaN values using input streams?
 

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  1. POIs it possible to read infinity or NaN values using input streams?
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    <p>I have some input to be read by a input filestream (for example):</p> <p><code>-365.269511 -0.356123 -Inf 0.000000</code></p> <p>When I use <code>std::ifstream mystream;</code> to read from the file to some </p> <p><code>double d1 = -1, d2 = -1, d3 = -1, d4 = -1;</code> </p> <p>(assume <code>mystream</code> has already been opened and the file is valid), </p> <p><code>mystream &gt;&gt; d1 &gt;&gt; d2 &gt;&gt; d3 &gt;&gt; d4;</code></p> <p><code>mystream</code> is in the fail state. I would expect </p> <p><code>std::cout &lt;&lt; d1 &lt;&lt; " " &lt;&lt; d2 &lt;&lt; " " &lt;&lt; d3 &lt;&lt; " " &lt;&lt; d4 &lt;&lt; std::endl;</code> </p> <p>to output </p> <p><code>-365.269511 -0.356123 -1 -1</code>. I would want it to output <code>-365.269511 -0.356123 -Inf 0</code> instead.</p> <p>This set of data was output using C++ streams. Why can't I do the reverse process (read in my output)? How can I get the functionality I seek?</p> <p>From MooingDuck:</p> <pre><code>#include &lt;iostream&gt; #include &lt;limits&gt; using namespace std; int main() { double myd = std::numeric_limits&lt;double&gt;::infinity(); cout &lt;&lt; myd &lt;&lt; '\n'; cin &gt;&gt; myd; cout &lt;&lt; cin.good() &lt;&lt; ":" &lt;&lt; myd &lt;&lt; endl; return 0; } </code></pre> <p>Input: <code>inf</code></p> <p>Output: </p> <pre><code>inf 0:inf </code></pre> <p>See also: <a href="http://ideone.com/jVvei">http://ideone.com/jVvei</a></p> <p>Also related to this problem is <code>NaN</code> parsing, even though I do not give examples for it.</p> <p>I added to the accepted answer a complete solution on ideone. It also includes paring for "Inf" and "nan", some possible variations to those keywords that may come from other programs, such as MatLab.</p>
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    1. COCan you read them all as strings and just convert?
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    2. COCould you make it a full example instead of half prose? Could you show whether infinity is printed at all? use `std::numeric_limits<double>::infinity()`
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    3. COShort of parsing the input yourself, I don't think so. The C++ streams are not guaranteed to be reversible
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