c - Does malloc() have a maximum return value? -


does size_t value of virtual memory pointer returned malloc() have upper boundary?

i wondering whether can safely set significant bit of 64 bits pointer indicate not pointer literal integer instead.

as @datenwolf's answer states, can't make assumptions how malloc providing memory address. msb may contain important bits overwrite, if attempted use them store meta data. have worked on 32-bit system returned addresses bits set in msb of addresses (not malloc, other system specific memory allocation functions).

however, is guaranteed malloc return address suitably aligned system. example, on 32-bit system, you'll 4-byte aligned pointer, , on 64-bit, you'll 8-byte aligned pointer. means guaranteed lower 2 or 3 bits respectively will zero. increase number of guaranteed bits using memalign instead. same effect storing meta data in significant bit. get/set literal, can up/down shift remaining bits.

however, wouldn't suggest either method. save heartache, , allocate little more memory store flag. unless you've got billions of them, it's not worth it.


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