Re: Preallocate ostringstream buffer


"Jason Winnebeck" <gillius-ng2@xxxxxxxxxxxxxxxxxx> skrev i meddelandet
news:esu8rpiXGHA.1228@xxxxxxxxxxxxxxxxxxxxxxx
P.J. Plauger wrote:
And it's generally unnecessary with the library shipped with VC++
these days, since the buffer grows exponentially. Execution time
is not a problem. If space limitations are a problem, it's still
particularly easy to use strstream with a preallocated buffer.

I've always wondered about this problem with exponential growth. A
common technique here is to always increase by a power-of-2, so the
argument that the time spent reallocating in insignificant compared
to the task itself, but this can become an issue with space. I
suppose you mention that in your last sentence, but is there a
better way in the general case? Probably not. I suppose worst case
scenario is that your program takes twice the memory than it needs.

A common compromise here is to grow by a factor of 1.5 instead of 2.
This halves the theoretical worst case, without affecting runtime much
at all. It also reduces memory fragmentation a bit.


Bo Persson


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