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  1. What way to store n.m matrix is more efficient? To create a vector of n vectors of size m or to a create big vector of size n.m?

  2. How is a vector of vectors stored in the memory? Does it contains only references/pointers or whole vectors?

IBazhov
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    I would prefer `std::vector<>(n * m)`. The vector itself is a structure of fixed size which stores size, length, and a pointer to data memory. The data memory is (re-)allocate on heap whenever resizing beyond capacity is requested. – Scheff's Cat Aug 06 '17 at 05:10

1 Answers1

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  1. It's more efficient to use a single vector of size N x M. This way all the memory is contiguous, and there is only a single pointer to all of it, rather than N pointers.

  2. A vector of vectors is stored as a pointer to an array of pointers, each of which points to an array of values.

John Zwinck
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    Apparently, the answer is not as obvious. https://stackoverflow.com/questions/33093860/using-nested-vectors-vs-a-flatten-vector-wrapper-strange-behaviour. – R Sahu Aug 06 '17 at 05:13