Is there a more efficient way to set a std::vector from a stream?

Question

Presently, I set the value of a std::vector from an std::ostringstream as follows:

void
foo(std::vector &am         


        

Answer 1

As pointed out in comments, your code is incorrect due to the two calls to str(). In order to improve efficiency you can avoid creating a temporary vector, like this:

void foo(std::vector &data, std::stringstream &stream) {
    const std::string& str = stream.str();
    data.assign( str.begin(), str.end() );
}

You can also avoid the std::string by using std::istreambuf_iterators:

void foo(std::vector &data, std::stringstream &stream) {
    data.assign(
        std::istreambuf_iterator( stream ), std::istreambuf_iterator()
    );
}

but given that those are input iterators, the vector has no chance to know how much data will be assigned and could perform a bit worse, as it cannot reserve enough space to avoid reallocations.