Initializing simple POD (members) / value_initialized

"Martin T." <>
Thu, 27 Aug 2009 15:38:28 CST
Hi all!

For holding various configuration data items, we are considering using
some structs that would look like so:

struct subject {
   size_t id;
   std::wstring name;
   double length;
   // ...

struct subject_list {
   std::wstring list_id;
   std::vector<subject> subjects;
   int position;

// ...

Now - I find it annoying, that to have proper default initialized POD
members, I would need to supply a default ctor that initializes all
members to zero. Bad for maintenance, as sooner or later someone will
forget to add a new member to the ctor list and then when a new struct
is used it ain't initialized properly.

When searching around, the only helper I found is
boost::value_initialized, but that is a more general approach for all
types and seems to be targeted at simplifying writing template code,
while what I want is as much transparency vs. the underlying POD type as
  possible. (No get() or explicit casts.)

So, I tried to come up with something myself. Feel free to comment!

* I think it should work for pointers, though I don't plan to use it for
* It's not important if not 100% portable, because I'll use this on
Windows only.

//! struct value_init
//! Wrapper type, for numerical PODS or pointers
template<typename T>
struct value_init {
T x;

//! Default initialize to zero
: x(0)
{ }

//! Note: default copy ctor and operator should be OK

//! from value
value_init(T val)
: x(val)
{ }

//! assign a value
T& operator=(T val) {
x = val;
return x;

//! convert to non-const underlying type
operator T&() {
return x;

//! convert to const underlying type
operator T const&() const {
return x;

//! make address-of operator return the pointer-type of the underlying type
//! (the numerical address value is the same anyway)
T* operator&() {
return &x;

//! const address-of operator
T const* operator&() const {
return &x;


// usage:
struct subject {
   value_init<size_t> id;
   std::wstring name;
   value_init<double> length;
   // ...


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