C++: Implementing Row Iterator for Table

I have a generic table class implemented in C++ that uses a shared_ptr< ptr_vector< vector<T> > > as its backing, where T is an arbitrary typename; the ptr_vector co开发者_运维问答ntains pointers to the vectors corresponding to the columns in the table. I decided to wrap the ptr_vector in a shared_ptr since the tables may contain many millions of rows, and the vectors containing data for each column in a ptr_vector for the same reason. (Please tell me if this can be improved.)

Implementing column-wise operations on this table is trivial, since I have access to the native iterator supplied by the vector. However, I also need the table to support row-wise operations: relatively mundane operations such as adding and removing rows should be supported, as well as the ability to use the STL algorithms with the table. Now, I have run across some design issues that I need some help to address:

1. It seems that implementing a custom iterator to conduct row-wise operations is necessary to accomplish what is describe above. Would boost::iterator_adaptor be the right way to go about doing this?
2. When the user adds rows to the table, I do not wish to impose a specific data structure upon the user -- how would I go about doing this? I am thinking of accepting iterators as parameters to the add_row() method.
3. If you think that I should be implementing this table structure differently, I am open to any suggestions that you may have for me. It was originally designed with the intent to store strings read from tab-delimited files containing hundreds of thousands of row entries.

Thank you very much for your help!

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The Boost library has a container called multi_array which provides and n-dimensional dynamic array which can be accessed and manipulated along each dimension. This seems to be very similar to what you are trying to build, perhaps you could use it instead?