What the heque is going on with the memory overhead of std::deque?

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Look at the code for _DEQUESIZ (number of elements per block):

#define _DEQUESIZ   (sizeof (_Ty) <= 1 ? 16 \
    : sizeof (_Ty) <= 2 ? 8 \
    : sizeof (_Ty) <= 4 ? 4 \
    : sizeof (_Ty) <= 8 ? 2 : 1)    /* elements per block (a power of 2) */

It gets smaller if the element is larger. Only for elements larger than 8 bytes will you get the expected behavior (percentual decrease of overhead with increase of element size).

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