Question

When thinking about this question I start to wondering if std::copy() and/or std::fill are specialized (I really mean optimized) for std::vector<bool>.

Is this required by C++ standard or, perhaps, it is common approach by C++ std library vendors?

Simple speaking, I wonder to know if the following code:

std::vector<bool> v(10, false);
std::fill(v.begin(), v.end(), true);

is in any way better/different than that:

std::vector<bool> v(10, false);
for (auto it = v.begin(); it != v.end(); ++it) *it = true;

To be very strict – can, let say: std::fill<std::vector<bool>::iterator>() go into internal representation of std::vector<bool> and sets their entire bytes instead of single bits? I assume making std::fill friend of std::vector<bool> is not a big problem for library vendor?

[UPDATE]

Next related question: can I (or anybody else 🙂 specialize such algorithms for let say std::vector<bool>, if not already specialized? Is this allowed by C++ standard? I know this will be non portable – but just for one selected std C++ library? Assuming I (or anybody else) find a way to get to std::vector<bool> private parts.

Answer 1

STD is headers only library and it is shipped with your compiler. You can look into those headers yourself. For GCC’s vector<bool> impelemtation is in stl_bvector.h. It probably will be the same file for other compilers too. And yes, there is specialized fill (look near __fill_bvector).