Re: STL string and assignment operator. Plz Help.

From:

Barry <dhb2000@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 01 Oct 2007 21:10:30 +0800

Message-ID:

<fdqv8b$sa5$1@news.cn99.com>

developer28 wrote:

Hi,

I would like to know the following.

suppose i write.

string str1 = "TestString";

string str2;

str2 = str1

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

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.

Now this makes me doubtful about the fact that internally both the
objects are using the same pointer.

[STD --
21.3.1 basic_stringconstructors

basic_string<charT,traits,Allocator>&
operator=(const basic_string<charT,traits,Allocator>& str);

16 Effects: If *this and str are not the same object, modifies *this as
effects:

data() points at the first element of an
allocated copy of the array whose
first element is pointed at by
str.data()

size() str.size()

capacity() a value at least as large as size()

If *this and str are the same object, the member has no effect.
--End-STD]

So std::string (basic_string<char>) does not share data with different
instances.

So the case you described here is not likely to happen if the
implementation is standard-conformed.