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POSQL-Like Selects in Imperative Languages
 

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    <p>I'm doing some coding at work in C++, and a lot of the things that I work on involve analyzing sets of data. Very often I need to select some elements from a STL container, and very frequently I wrote code like this:</p> <pre><code>using std::vector; vector&lt; int &gt; numbers; for ( int i = -10; i &lt;= 10; ++i ) { numbers.push_back( i ); } vector&lt; int &gt; positive_numbers; for ( vector&lt; int &gt;::const_iterator it = numbers.begin(), end = numbers.end(); it != end; ++it ) { if ( number &gt; 0 ) { positive_numbers.push_back( *it ); } } </code></pre> <p>Over time this for loop and the logic contained within it gets a lot more complicated and unreadable. Code like this is less satisfying than the analogous SELECT statement in SQL, assuming that I have a table called numbers with a column named "num" rather than a std::vector&lt; int > :</p> <pre><code>SELECT * INTO positive_numbers FROM numbers WHERE num &gt; 0 </code></pre> <p>That's a lot more readable to me, and also scales better, over time a lot of the if-statement logic that's in our codebase has become complicated, order-dependent and unmaintainable. If we could do SQL-like statements in C++ without having to go to a database I think that the state of the code might be better. </p> <p>Is there a simpler way that I can implement something like a SELECT statement in C++ where I can create a new container of objects by only describing the characteristics of the objects that I want? I'm still relatively new to C++, so I'm hoping that there's something magic with either template metaprogramming or clever iterators that would solve this. Thanks!</p> <p>Edit based on first two answers. Thanks, I had no idea that's what LINQ actually was. I program on Linux and OSX systems primarily, and am interested in something cross-platform across OSX, Linux and Windows. So a more educated version of this question would be - is there a cross-platform implementation of something like LINQ for C++?</p>
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