Shrink to Fit
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## Shrink to Fit

From GCC 3.4 calling `s.reserve(res)` on a `string s` with `res < s.capacity()` will reduce the string's capacity to `std::max(s.size(), res)`.

This behaviour is suggested, but not required by the standard. Prior to GCC 3.4 the following alternative can be used instead

          std::string(str.data(), str.size()).swap(str);

This is similar to the idiom for reducing a `vector`'s memory usage (see this FAQ entry) but the regular copy constructor cannot be used because libstdc++'s `string` is Copy-On-Write.

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