Re: Using malloc in C++

From:

Stuart Golodetz <blah@blah.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 28 Jun 2010 13:31:25 +0100

Message-ID:

<9JCdnW6KG5iAC7XRnZ2dnUVZ8qidnZ2d@pipex.net>

On 28/06/2010 12:20, Bharath wrote:

Hi all,

I am trying to use malloc to allocate memory to an object. Something
like:

TestClass *obj = (TestClass *) malloc(sizeof(TestClass));

Its obvious that the constructor doesn't get called in the above case,
nor the destructor when I free it.

Is there a way that I can invoke the constructor after the malloc
statement?

I believe that's what 'new' does isn't it? It allocates memory and
then invokes the constructor.

Thanks,
-Bharath

#include <iostream>
#include <memory>

struct X
{
    X() { std::cout << "X()\n"; }
    ~X() { std::cout << "~X()\n"; }
};

void test_malloc()
{
    X *p = static_cast<X*>(malloc(sizeof(X)));
    new (p) X;
    p->~X();
    free(p);
}

void test_operator_new()
{
    X *p = static_cast<X*>(::operator new(sizeof(X)));
    new (p) X;
    p->~X();
    ::operator delete(p);
}

void test_new()
{
    X *p = new X;
    delete p;
}

int main()
{
    test_malloc();
    test_operator_new();
    test_new();
    return 0;
}

Cheers,
Stu