Re: Is this type of char array initization legal?

From:

Victor Bazarov <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Fri, 24 Oct 2008 16:18:56 -0400

Message-ID:

<gdtajg$6rp$1@news.datemas.de>

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).>>

To me it's pretty clear. Each character from the literal initialises
its respective element of the array. The terminating null character
does initialise the corresponding element of the array *too*. If there
are fewer characters in the literal than elements in the array (which is
an aggregate), the rest of the array elements are zero-initialised.

V
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