reduce the capacity of an stl vector

Question

Is there a way to reduce the capacity of a vector ?

My code inserts values into a vector (not knowing their number beforehand), and when this finishes, the vectors are used only for read operations.

I guess I could create a new vector, do a .reseve() with the size and copy the items, but I don't really like the extra copy operation.

PS: I don't care for a portable solution, as long as it works for gcc.

Answer 1

std::vector<T>(v).swap(v); 

Swapping the contents with another vector swaps the capacity.

  std::vector<T>(v).swap(v); ==> is equivalent to    std::vector<T> tmp(v);    // copy elements into a temporary vector          v.swap(tmp);              // swap internal vector data 

Swap() would only change the internal data structure.

Answer 2

With C++11, you can call the member function shrink_to_fit(). The draft standard section 23.2.6.2 says:

shrink_to_fit is a non-binding request to reduce capacity() to size(). [Note: The request is non-binding to allow latitude for implementation-specific optimizations. —end note]