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    <p>Your rule declares the wrong exposed attribute. Change it:</p> <pre><code>qi::rule&lt;std::string::const_iterator, std::vector&lt;float&gt;(), iso8859::space_type&gt; vertex; </code></pre> <p>However, since you don't template your grammar struct on anything (like iterator/skipper type), it makes no sense to have a grammar struct. Instead, let <code>phrase_parse</code> simply deduce the iterator, skipper and rule types all at once and write:</p> <pre><code>bool parseObj(std::string const&amp; data, std::vector&lt;float&gt; &amp;v ) { return qi::phrase_parse( data.cbegin(), data.cend(), 'v' &gt;&gt; qi::float_ &gt;&gt; qi::float_ &gt;&gt; qi::float_, qi::space, v); } </code></pre> <p>I think you'll agree that's more to the point. And as a bonus, it "just works"(TM) because of the awesomeness that is <em>automatic attribute propagation</em> rules.</p> <p>However, seeing your grammar, you'll certainly want to see these:</p> <ul> <li><p><a href="https://stackoverflow.com/questions/17465061/how-to-parse-space-separated-floats-in-c-quickly/17479702#17479702">How to parse space-separated floats in C++ quickly?</a> showing how to parse into a vector of structs </p> <pre><code>struct float3 { float x,y,z; }; typedef std::vector&lt;float3&gt; data_t; </code></pre> <p>with little or no extra work. Oh and it benchmarks the spirit approach reading a 500Mb file against the competing <code>fscanf</code> and <code>atod</code> calls. So, it parses multiple lines at once :)</p></li> <li><p>Use the <code>qi::double_</code> parser instead of <code>qi::float_</code> <em>even if you're ultimately assigning to single-precision <code>float</code> variables</em>. See <a href="https://stackoverflow.com/questions/17391348/boost-spirit-floating-number-parser-precision/17393048#17393048">Boost spirit floating number parser precision</a></p></li> </ul>
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    1. COGreat answer! Thank you very much. So what you're saying in the beginning is that I should only use grammar structs if I use templates? Another question: how can I implement multiple rules when using phrase_parse the way you describe? Because eventually I also want to parse floats preceded by "vn" and "vt", which are all in the same *.obj file. Do I just run the phrase_parse function for each separate rule? Thx :)
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    2. CO@KrienLinnenbank I was saying the grammar struct wasn't pulling it's weight. There _are_ more reasons to have grammar structs, but you wouldn't have it locally defined then, anyways.
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    3. CORegarding the second question: I'd split out a grammar struct anyways, and parse your grammar _as it is_ (that's what you use a parser generator for, after all!). I.e. I'd **not** run separate lines through separate rules. Perhaps you should make it a question if you get stuck. (For now, be sure to visit the first linked other answer for ideas)
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