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POSTL vector: When vector capacity is increased due to insert, does the old contiguous memory deleted or kept after allocating new contiguous memory?
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2013-08-02T07:11:19.777
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Recently got into confusion on whether old memory will be freed or not after STL::vector size is increased. When stl::vector capacity is increased due to insert, a new contiguous memory is allocated (=2*current vector capacity) and old contents are copied to new memory. And the old memory is freed. Now recently we get into discussion and some believe that old memory is not freed instead it is kept for reference. So over multiple resize's the stl::vector start accumulating memory which is not really needed. To my understanding it frees old memory but I don't have any concrete documentation on it. However my understanding may be wrong! I would appreciate if anyone who knows the details, share the same!
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STL vector: When vector capacity is increased due to insert, does the old contiguous memory deleted or kept after allocating new contiguous memory?
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1. COIf you are concerned about whether the memory is actually freed or not, you might want to use a profiler or break on `free()` or `operator delete()` with a debugger to see what's actually happening. I believe that most implementations will allocate a new array, copy everything, and delete the old one, but this is implementation defined, so I don't know. Performancewise, this approach is of course bad because the moving necessitates a lot of move constructors being called, with all the overhead that entails. I believe you can count on the implementation _not_ calling `realloc()` internally.
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