alt Hacker NewsAn array of arrays is an extremely inefficient and error-prone way to represent multidimensional arrays.
If I want a 1000x1000 array, representing it physically as a single 1000000-element array requires one allocation, and processing it element-by-element (assuming it's stored in the same order we're iterating over it) is sequential in memory and therefore very efficient.
Representing it as 1000 separate 1000-element arrays requires 1000 allocations, and pointer-chasing every time we move from one row to the next.
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nish__ • yesterday at 5:23 PM
I see. That makes sense.
Isn't an array of arrays by definition the sequential implementation?
Otherwise you would have an array of pointers to arrays. The usage (syntax) for them would be the same but the performance would not be.
They also have different uses. You would expect an array of arrays to be an array of arrays which share the same length. For an array of pointers to an array you would expect dynamic length arrays contained within the original array.
Even in c++ could you not just define some int [1000][1000]foo? I've never really used C++ but my C knowledge assumption is that is 1000000 continuous elements.