Re: STL string and assignment operator. Plz Help.
On Oct 1, 1:40 pm, developer28 <aman.k.se...@gmail.com> wrote:
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.
No. It varies from one implementation to the next.
actually i do something like
const char * temp = str1.c_str();
Which is something completely different.
that converts it to a c type string.
and then when i modify the contents of temp, it also affects str2.
I doubt it. You mean that if later, you do something like:
temp = NULL ;
, the contents of str2 (or str1) change? I've never seen
anything like that, and I don't see how it could be.
Technically, you cannot modify anything through temp, since it
points to const. The next version of the standard will have a
non-const data() function, however, which is expressedly
designed to allow modification of the string, e.g. by legacy C
functions which take char* as pointers to a buffer. In
practice, you can reliably use this today as well, by casting
away the const on the pointer returned by data(), or by using
&str[0]. It is, however, very dangerous; any modifications
beyond str.size() will result in immediate undefined behavior.
It should only be used when interfacing with legacy code.
And of course, what happens in str.data() has nothing to do with
assignment.
Now this makes me doubtful about the fact that internally both
the objects are using the same pointer.
The specifications of std::basic_string are fairly complicated,
intentionally, in order to allow different implementations. The
user visible semantics, however, are fairly clear, and that's
all you need to worry about.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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