Re: Is this type of char array initization legal?

From:

Pete Becker <pete@versatilecoding.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 24 Oct 2008 16:46:31 -0400

Message-ID:

<2008102416463116807-pete@versatilecodingcom>

On 2008-10-24 16:18:56 -0400, Victor Bazarov <v.Abazarov@comAcast.net> said:

Pete Becker wrote:

On 2008-10-24 12:49:25 -0400, Victor Bazarov <v.Abazarov@comAcast.net> said:

DomoChan@gmail.com wrote:

the code below will compile in visual c++ 2003, but im not sure its
valid.

unsigned char myString[200] = "";

after this line executes, all the bytes within myString are indeed set
to '0's' but is this really valid c++ or c? where can I find out how
this is implemented?

Im concerned because I had a 3rd party library wrapper which was
crashing, and I was able to alleviate the crash by changing the
initialization method from the above to ...

unsigned char myString[200];

memset( myString, 0, sizeof( myString ) );

any guidance is greatly appreciated!

It is valid. Allowed explicitly by the Standard, subclause 8.5.2.

The only reason it could be crashing is if the compiler wastn't
providing proper initialisation for the array. What you could do is
revert this to what it was and put an assertion to see if it's indeed
the problem:

     unsigned char myString[200] = "";
#ifndef NDEBUG
     for (int iii = 0; iii < 200; ++iii)
        ASSERT(myString[iii] == 0);
#endif

Hmm, is this required if the char array has automatic storage duration?
I have always assumed that it wasn't, that only the characters
corresponding to characters in the initializer would be initialized,
but it doesn't seem completely clear from a quick glance at the
standard.

8.5.1/7:
<<If there are fewer initializers in the list than there are members in
the aggregate, then each member not
explicitly initialized shall be value-initialized (8.5).>>

Well, yes, that's the requirement for aggregate initialization. But
does aggregate initialization apply here? Aggregate initialization is
indicated by "a brace-enclosed, comma-separated list ...", which isn't
present here. I don't see anything in 8.5.2 [dcl.init.string] that says
that aggregate initialization is used, although the "optionally
enclosed in braces" hints that it may be.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)