std::vector::reserve performance penalty

Question

inline void add(const DataStruct& rhs) {
   using namespace boost::assign;
   vec.reserve(vec.size() + 3);
   vec += rhs.a, rhs.b, rhs.c;
}

The

Answer 1

Move the reserve outside of the add.

Each time you invoke "add", you are reserving atleast 3 extra elements. Depending on the implementation of vector, this could be increasing the size of the backing array almost every time you call "add". That is would definately cause the performance difference that you describe.

The correct way to use reserve is something like:

vec.reserve(max*3);
for(int i=0; i