Is it better to allocate memory in the power of two?

Question

When we use malloc() to allocate memory, should we give the size which is in power of two? Or we just give the exact size that we need?
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Answer 1

When I'm allocating a buffer that may need to keep growing to accommodate as-yet-unknown-size data, I start with a power of 2 minus 1, and every time it runs out of space, I realloc with twice the previous size plus 1. This makes it so I never have to worry about integer overflows; the size can only overflow when the previous size was SIZE_MAX, at which point the allocation would already have failed, and 2*SIZE_MAX+1 == SIZE_MAX anyway.

In contrast, if I just used a power of 2 and doubled it each time, I might successfully get a 2^31 byte buffer and then reallocate to a 0 byte buffer next time I doubled the size.

As some people have commented about power-of-2-minus-12 being good for certain malloc implementations, one could equally start with a power of 2 minus 12, then double it and add 12 at each step...

On the other hand if you're just allocating small buffers that won't need to grow, request exactly the size you need. Don't try to second-guess what's good for malloc.