A POD struct is not correctly initialized when default
initialization is requested in the initialization list of a
constructor, and it is a base class.  Consider the following
program:

-------------------------------------------------

#include <iostream>
#include <memory>
#include <stdlib.h>
#include <string.h>

void*
operator new( size_t n ) throw (std::bad_alloc)
{
    void*               p = malloc( n ) ;
    if ( p == NULL ) {
        throw std::bad_alloc() ;
    }
    memset( p, 0xAA, n ) ;
    return p ;
}

void
operator delete( void* p ) throw ()
{
    free( p ) ;
}

struct POD
{
    short               l ;
    unsigned char       s[ 6 ] ;
} ;

class A : public POD
{
public:
    A() : POD() {}
} ;

class B
{
public:
    B() : myPOD() {}
    POD myPOD ;
} ;

int
main()
{
    A* pA = new A ;
    std::cout.setf( std::ios::hex, std::ios::basefield ) ;
    std::cout << "length A = " << pA->l << std::endl ;
    B* pB = new B ;
    std::cout << "length B = " << pB->myPOD.l << std::endl ;
    return 0 ;
}
-------------------------------------------------
(The replacement new and delete are just to ensure that the
memory doesn't accidentally happen to be correctly initialized.)

According to the standard, "An object whose initializer is an
empty set of parentheses, i.e., (), shall be
default-initialized", and default initialization of a POD type
is zero-initialization.  When compiled, however, this program
outputs:

-------------------------------------------------
length A = aaaa
length B = 0
-------------------------------------------------

The default initialization has correctly taken place for the
member object, but not for the base class.

-- 
James Kanze (GABI Software)             email:james.kanze@gmail.com
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