Re: How to init array of strings member by a constructor?

From:

Alex Blekhman <xfkt@oohay.moc>

Newsgroups:

microsoft.public.vc.language

Date:

Sun, 29 Oct 2006 14:05:00 +0200

Message-ID:

<uv6$AK1#GHA.2300@TK2MSFTNGP04.phx.gbl>

David F wrote:

I have recalled in the meanwhile that it has nothing to
do with arrays of strings but it has to do with any array,
and more precisely with any aggregate member.
It is by the language definition as mention in the TC++PL book.
Since initialization is not the same as assignment - an
explicit constructor's initialization list can only initialized
what the default constructor can and it has to be an entire member.
Hence, can't init individual elements of a vector for example.
In the way you described, which is like statements of any
function, you can issue ASSIGNMENT statement which
can be applied as usual.

Yes, you're right. Initialization of aggregates is performed
by copy initialization and equivalent to the form:

     T var = value;

So, strictly speaking, following initialization:

     std::string arr[3] = { "a", "b", "c" };

should be performed via temporary copy (in pseudocode):

     std::string tmpA("a");
     std::string tmpB("b");
     std::string tmpC("c");

     std::string* arr = malloc(sizeof(std::string) * 3);
     std::string::string(arr + 0, tmpA);
     std::string::string(arr + 1, tmpB);
     std::string::string(arr + 2, tmpC);

However, in the case above compiler is allowed to eliminate
redundant temporary copy and construct target object from
initial value directly.

HTH
Alex