Re: Protecting against uninitialized variables

Greg Herlihy <>
Mon, 19 Mar 2007 13:22:01 CST
On 3/18/07 10:05 PM, in article, "Tim Conkling"
<> wrote:

The compiler I use (Visual C++ 2003) warns when I am reading from a
potentially uninitialized variable, unless that variable is a class

struct Foo { int x; };

void foo()
   Foo myFoo;
   printf("%d", myFoo.x); // undefined output

(I'm not sure if there are compilers out there that warn about this
problem; mine definitely does not.)

The gcc compiler has a setting to enable such a warning.

This has caused headaches in projects I've worked on, especially since
this sort of error isn't caught in Debug builds, making it hard to
notice & track down. To protect against this sort of error, I've
created a templated class called "safe_type," and I'm looking for
comments on its design -- possible issues, whether it's useful, etc.

template <class T>
struct safe_type_traits;

struct safe_type_traits<bool>
static bool DefaultValue() { return false; }

struct safe_type_traits<int>
static int DefaultValue() { return 0; }

struct safe_type_traits<float>
static float DefaultValue() { return 0.0f; }

If each type requires its own safe_type specialization, then there is little
benefit in declaring safe_type a class template instead of three separate
classes - one for each of the target types. But the specializations are not
needed, it's possible to write one template capable of zero-initializing all
three types (and any other fundamental type).

template <class T>
struct safe_type_traits<T*>
static T* DefaultValue() { return NULL; }

template <class T>
struct safe_type
T m_val;

safe_type() : m_val(safe_type_traits<T>::DefaultValue()) {}
safe_type(T val) : m_val(val) {}

safe_type& operator=(safe_type rhs) { m_val = rhs.m_val; return
*this; }
safe_type& operator=(T rhs) { m_val = rhs; return *this; }

// conversion operator
operator T() const { return m_val; }

// operator ->
T operator->() const { return m_val; }

// operator ==
template <class U> bool operator==(U rhs) { return (m_val == rhs); }

// operator !=
template <class U> bool operator!=(U rhs) { return (m_val != rhs); }

// operator +=
template <class U> safe_type& operator+=(U rhs)
m_val += rhs;
return *this;

[ of implementation omitted]

In my view this solution is over-engineered - it goes far beyond what is
required to ensure the zero-initialization of a fundamental type serving as
a class member. I would think that a more pared-down implementation would do
the job:

     template <class T>
     struct safe_type
         safe_type() : value(T()) {}

         operator T&() { return value; }
         T value;

     typedef safe_type<int> safe_int;

     struct C
         C() {}
         safe_int i;

     using std::cout;

     int main()
         C c;

         cout << c.i << "\n";
         cout << c.i + 5 << "\n"; // safe_int may appear in expressions

     Program Output:


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