"Jim Langston" <>
Sat, 23 Jun 2007 09:10:05 -0700
"Mohitz" <> wrote in message

Ya, the failure of the condition indicates a parse error. I want to
just print an intelligent
error message when that happens and want the program to exit. What's
the best way to do that?

Also, I am now trying to return a pointer but the program exits with a
segmentation fault. I am sorry
i am not quite good with pointers. Here is the code i am using. Is
something wrong with it?

Nothing is wrong with this code, per se (see my comments inline about
calling new and not delete), that I can see. Nothing that should cause a
segmentation fault. Is your class assignable? Does it have a custom
assignment operator? It may need one if you are using pointers, references
or use of new in the class constructor or initalizer.

I would quesiton if deques are assignable (your statement: deque<ClassName>
tempDeque = someGlobalClassNameDeque). It is also not required. Just use
someGlobalClassNameDeque in place of tempDequie inside your code.

Also, your method of assigning a newed instance the value from an iterator
is convoluted. You are using an extra temp variable you don't need to.
Instead of:
   ClassName temp = *tempDequeIterate;
   *tempClassName = temp;
you can just use
   *tempClassName = *tempDequeiterate;
as I've shown in my "why don't you do it this way" code.

ClassName * funcName(string name)
     deque<ClassName> tempDeque = someGlobalClassNameDeque;
     deque<ClassName>::iterator tempDequeIterate;
     tempDequeIterate = tempDeque.begin();
     while (tempDequeIterate != tempDeque.end())
        ClassName * tempClassName = new ClassName();

Here's new, where's your delete? I wouldn't bother creating a new instance
and returning it unless you have to though.

        ClassName temp = *tempDequeIterate;
        *tempClassName = temp;
        if (name == temp->name)
                return tempClassName;

How about instead of those 5 lines above (untested code):

   if ( name == tempDequeIterate->name )
      ClassName* tempClassName = new ClassName();
      *tempClassName = *tempDequeIterate;
       return tempClassName;

That way you only call new once for the object you are going to return and
dont' need to call delete on it in this function

     return NULL;

int main()
       ClassName * p = funcName(someString);
       if (p == NULL)
           parseError(someString + " undefined.");
           toRet = anotherFunc(*p);
       return toRet;

Any suggestions/comments would be appreciated.

At this point it is difficult to say what is causing your segmentation
fault. Like I said, it is most likely in your assignment operator, unless I
am missing something obvious. Or maybe it is actually an out of memory
error with all the news and no deletes?

Can you post some code that will compile and produce the error?

On Jun 22, 3:08 am, Rolf Magnus <> wrote:

Mohitz wrote:

How do you write a function in C++ which returns a class object in
some cases and in others, returns something like a NULL pointer so
that i can know in the callee function that the object doesnt exist??

ClassName A()
   ClassName a;
   if (condition)
        return a;

          throw some_exception();

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