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POhidden copy in STL vector?
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copied!<p>I am experiencing unexpected performance degradation when using vectors with classes.</p> <p>I have a csv_File class that reads in a csv file and stores the contents in a 2D vector. There's a member function that allows access, e.g.</p> <pre><code> csv_File file("file.csv"); file.access(2,2); </code></pre> <p>To access the 2,2 element.</p> <p>Then, I have another class csv_Array that stores multiple csv_File objects in a vector, e.g private member vector There's a member function that allows access, i.e. it returns a csv_File object, for example:</p> <pre><code> csv_Array file_array(5); //store 5 csv_File objects file_array.grab(0).access(2,2); </code></pre> <p>In the second line, grab returns a csv_File object (in this case, the first one) and access is a member function of the csv_File object.</p> <p>However, I have noticed that the call csv_Array.grab(0).access(2,2); is much slower than it should be (it should be just 3 vector::at calls).</p> <p>Is there some sort of hidden copy going on that is making this very slow?</p> <p>EDIT: Here are some of the relevant function prototypes:</p> <pre><code> //Access in csv_File std::string access(int row, int column); //grab in csv_Array and csv_Analysis (mentioned below) csv_File grab(int index); </code></pre> <p>ADDITIONAL DETAILS (if necessary): The application of this code is to load a bunch of csv files into memory before passing it to a friend class that will do some calculations with the data. Schematically, I have the following:</p> <p>1) csv_Array has private member vector storage; 2) csv_Analysis is a class that is a friend of csv_Array 3) csv_Analysis accesses vector storage, which is in csv_Array 4) This access is done by passing csv_Analysis a reference to storage in csv_Array (so no copy hopefully....), e.g public: csv_Analysis(csv_Array &csv_block);</p> <p>Thus, the call given above[file_array.grab(0).access(2,2); ] actually has one additional class "level" in between and is more like</p> <pre><code> csv_Analysis analysis_Object(file_array); analysis_Object.grab(0).access(2,2); </code></pre> <p>where grab acts in the same way, and is also defined as a member function of csv_Analysis class.</p>

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