Re: STL string and assignment operator. Plz Help.

From:

Juha Nieminen <nospam@thanks.invalid>

Newsgroups:

comp.lang.c++

Date:

Tue, 02 Oct 2007 20:16:53 +0300

Message-ID:

<47027daa$0$3218$39db0f71@news.song.fi>

developer28 wrote:

string str1 = "TestString";

string str2;

str2 = str1

Now can someone tell me how this assignment operator works internally.

  It depends on the compiler.

  Some compilers implement std::string copying by using the
copy-on-write technique. This means that only the pointer is copied and
a reference count incremented. (The deep copy is made only if you try to
modify one of the strings.)

  Other compilers do a deep copy.

  The standard doesn't enforce any specific method to be used.

actually i do something like

const char * temp = str1.c_str();

that converts it to a c type string.

and then when i modify the contents of temp, it also affects str2.

As people have told you, you shouldn't do that. You are modifying
the data behind a const pointer, which is asking for trouble.

Anyways, this would indicate that the compiler you are using is using
copy-on-write for std::string (and you are circumventing it with your
modifying-const-data hack).