When does std::string allocation take place on initialization

Question

When I create a std::string member variable in a class, will there be already a default memory allocated when it is instantiated? Or does std::string defer allocation until it is actually used?

I'm using Visual Studio 2010 at the moment, and I noticed, when I create an empty string with:

  std::string s0;
  std::string s1 = "";

Both have capacity == 15 set. So does this mean that it already allocated 15 bytes of memory? If yes, can I prevent this so that no memory is allocated?

Would this be implementation specific across different compilers?

Answer 1

The initial capacity of an empty std::string is unspecified by the standard, and is implementation dependent.

Many implementations will allocate an initial capacity of around 16 or so characters (and yes, the capacity refers to allocated memory).