Is there a fast way to replace two map contents?

In my code I h开发者_运维知识库ave a map which holds a large amount of data (~100MB) I need to copy all that data from one map to another. currently I am doing this with swap but to my understanding, swap is a fancy way to do a copy. Is there a way to simply transfer the memory used by the two maps? I think that I can do this with pointers but I was hoping for a more elegant way.

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23.2.1 [container.requirements.general] of ISO/IEC 14882:2011 contains a list of general container requirements. For all standard containers the expressions a.swap(b) and swap(a, b) must exchange the contents of a and b and for all standard containers other than array both must have constant time. This effectively means that swapping maps cannot involve copying all the map elements.

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Unless this came up in a profiler run as a bottleneck, you may be optimizing prematurely.

My compiler's std::map::swap() has the following comment, which indicates that a map swap is likely to be very fast:

  /**
   *  This exchanges the elements between two maps in constant
   *  time.  (It is only swapping a pointer, an integer, and an
   *  instance of the @c Compare type (which itself is often
   *  stateless and empty), so it should be quite fast.)  Note
   *  that the global std::swap() function is specialized such
   *  that std::swap(m1,m2) will feed to this function.
   */

(g++ 4.4.5)