Re: Differences between C++ 'new' operator and 'malloc()' (NOT a C/C++ question)

["Claude SIMON" <sc dot cygwin dot com at zeusw dot org>]

Ryan Johnson wrote:
> On 04/07/2012 5:45 AM, Claude SIMON wrote:
>> When I compile the component with Visual C++, it works. When I compile
>> the
>> component with g++... it crashes.
>>
>> With 'gdb', I found that the problem happens when calling the 'malloc'
>> function (as soon as the function is called, NOT when the returned
>> allocated memory is used). When I replace the 'malloc' by a the C++
>> 'new'
>> operator, the component compiled with Cygwin g++ doesn't crash anymore.
>
>> I thought that the C++ 'new' operator calls the 'malloc' function, but
>> this seems not to be the case. As I want to use 'malloc'-like functions
>> rather than the C++ 'new' operator, I wonder which functions are used in
>> the C++ 'new' operator to allocate memory (and naturally which functions
>> are used in the C++ 'delete' operator to free the memory).
> Operator new() and malloc() are explicitly *not* interchangeable (for
> many reasons, not least of which that the Standard says so). If you were
> to free new'ed memory, or delete malloc'ed memory, the resulting heap
> corruption could easily manifest as a crash the next time you tried to
> allocate something... or it might just silently clobber data and lead to
> "spooky action at a distance."
>

Thank you for the answer, but I am aware of this and my problem has
nothing to do with it, nor, as stated in the subject, with having some
lacuna in C/C++ programming.

Let's try to be a little more explicit despite my poor English.

Let's consider a Java native component which only calls a 'malloc(1)'. It
doesn't even test the returned value (it is usually not a good idea, but
it doesn't matter here).

This component :
- compiled with g++ under Linux : works,
- compiled with g++ under Mac OS : works,
- compiled with Visual C++ under Windows : works,
- compiled with g++ under Cygwin : CRASHES !

It crashes as soon the 'malloc(1)' function is called. You don't even have
the opportunity to test the returned value, nor to use it. It's perhaps a
Cygwin bug, or perhaps a JVM/JRE/JDK bug ; I don't know and I don't bother
(but if someone will make some investigation about that, I'm ready to help
him or her if I can).

When you replace the 'malloc()' by the 'new' operator, then the component
compiled with g++ under Cygwin works too.
The 'new' operator, among other things, allocates memory, as 'malloc()'
does, but obviously it doesn't use 'malloc()' as it doesn't crash. So,
because I can't use 'malloc()' in my Java native components, and because I
doesn't want to use the 'new' operator, I wish to know which functions the
'new' operator uses to allocate memory, so I can use them in my Java
native component so they would no more crash when compiled with g++ under
Cygwin.

-- 
Claude SIMON (sc.cygwin.com@zeusw.org)


--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple