Re: checking if the memory was allocted previously

From:

=?ISO-8859-1?Q?Marcel_M=FCller?= <news.5.maazl@spamgourmet.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 09 Jun 2010 11:46:54 +0200

Message-ID:

<4c0f630f$0$6778$9b4e6d93@newsspool3.arcor-online.net>

Hi!

mjoachimiak wrote:

//////////////////////////
mystrucure *dynamic_element = NULL

void some_function()
{
if (dynamic_element == NULL)
dynamic_element = malloc(sizeofm(mystructure));
if (dynamic_element != NULL) do_smth(dynamic_element);
}

If you use C++ you should prefer new/delete over malloc where possible.
This eliminates the need for the second NULL check since new will not
return NULL.

main()
{
call some_function() many times;
if (dynamic_element != NULL)
free(dynamic_element);
}
/////////////////////////////
what about my previous memory allocation ?
Can it cause race condition also?

Yes, if and only if "call some_function() many times" calls
some_function in parallel.

You should put the initialization of dynamic_element in main before the
other processing. This would completely eliminate the need for the NULL
checks in some_funtion.

However, the content of mystructure has to be accessed synchronized or
atomic or read only anyway if you intend to operate in parallel without
race conditions.

Marcel