From: alainm AT news DOT RISQ DOT QC DOT CA (Alain Magloire)
Subject: Re: djgpp strangeness
Newsgroups: comp.os.msdos.djgpp
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Date: Thu, 23 Dec 1999 16:42:54 GMT
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Weiqi Gao (weiqigao AT a DOT crl DOT com) wrote:
: Alain Magloire wrote:
: > 
: > If you are writting in C++, then do.  If you want to use C, then use C.
: > malloc/free are not the preferred way to allocate objects and manage memory,
: > in C++.
: > 
: > I do not remember what the std say, but malloc() will give
: > uninitialized memory, and free () is not even require to invoke the
: > destructor, when the object is collected.
: > 
: > Use new and delete.

: I was thinking along the same lines when I tested my theory out with the
: following program:

: ==========8<==========8<==========8<==========
: #include <iostream>
: #include <cstdlib>

: class X {
:   int i;
: public:
:   X(int i_) : i(i_) {}
:   void foo() { cout << "i = " << i << endl; }
:   void setI(int i_) { i = i_; }
: };

: int main() {
:   X *xp = (X *) malloc(sizeof(X));
:   xp->setI(100);
:   xp->foo();
: }
: ==========8<==========8<==========8<==========

: And it worked!  It's bad style, I know, but does not generate any
: errors, and prints out '100' as expected.

: Valkir's classes might be more complicated than the one above, which
: could cause an error when used with malloc().

No, that is not my point, the point is malloc()/free() will not
call the constructor or destructor of a class, reread the post.  Try this
maybe it will be clearer. As you will see the destructor is not call.
If not try comp.lang.c++, they will go more in details.
here, '%' is my prompt.

% uname -rs
SunOS 5.6
% cat mine.cc
#include <iostream>
#include <cstdlib>

class X
{
  public:
    X()  { cout << "counstructor call" << endl; }
    ~X()  { cout << "destructor call" << endl; }
    void foo() { cout << "method" << endl; }
};

int main()
{
  cout << "----------------using malloc/free----------------" << endl;

  X *xp = (X *)malloc (sizeof(X));
  xp->foo();
  free (xp);

  cout << "----------------using new/delete----------------" << endl;

  X *xx = new X();
  xx->foo();
  delete xx;
  return 0;
}
% g++ -o mine mine.cc
% ./mine
----------------using malloc/free----------------
method
----------------using new/delete----------------
counstructor call
method
destructor call

--
au revoir, alain
----
Aussi haut que l'on soit assis, on est toujours assis que sur son cul !!!