Re: new(nothrow not even from constructor)

"Bo Persson" <>
Sun, 19 Dec 2010 13:14:46 +0100
Virchanza wrote:

   I've been looking through the Dinkumware reference manual and I
can't find a form of "new" that doesn't throw any exceptions at all.

   I'm currently writing a program that uses the "new" operator to
do stuff like create thread objects and window objects. If a thread
object or window object can't be created, my program displays a
message box, something like "Creation of the Help dialog box
failed". Ideally it would be:

   Thread *const p = new(std::nothrow) Thread(my_entry_function,

   if (!p)
       wxMessageBox("Can't create thread");

The problem with this however, is that don't want any exceptions at
all to be thrown by the "new" operator. For instance, the following
"Hello World" program doesn't work:

#include <new>
#include <iostream>

class MyClass {

       throw 5;

int main()
   MyClass *p = new(std::nothrow) MyClass();

   std::cout << "Hello World!\n";

The "nothrow" only stops "new" from throwing a "bad_alloc" if the
memory allocation fails -- it doesn't suppress exceptions thrown
from the constructor of the object. (Or at least that's the GNU C++

It DOES stop "new" from throwing, it just doesn't stop "MyClass()"
from throwing. .-)

What about

    MyClass *p = new(std::nothrow) MyClass(std::nothrow);


Is the following my only option?

int main()
   MyClass *p;

   try { p = new MyClass(); } catch(...) { p = 0; }

   std::cout << "Hello World!\n";

Pretty much, yes.

Another thing to consider is that if "new" or "MyClass" throws because
of lack of resources, what are the odds that wxMessageBox will work at
that point? Isn't that trying to create a window telling you that
creating a window just failed?!

Bo Persson

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