GCC-specific casting warnings

[Stewbond]

I have a class containing this:

class MyClass
{
  void* m_value;
  int m_type;
public:
  template <typename T>
  T GetVal(T p_default)
  {
    if (!m_value)
      return p_default;

    switch(m_type)
    {
      case 1: case 21:
        return (T)(*((char*)m_value));
      case 2: case 22:
        return (T)(*((bool*)m_value));
      case 3: case 23:
        return (T)(*((short*)m_value));
      case 4: case 24:
        return (T)(*((float*)m_value));
      default:
        return p_default;
    }
  }
};

I'm dereferencing a pointer to a stored type and casting it to the templated type. It compiles file in VS without warnings.

In GCC I get compiler warnings about loss of precision/truncation whenever I add a bool as the templated type. Do you know how I can make this GCC-safe?

I've noticed VS handles this nicely for casting:T(value)
but GCC needs this:(T)value
That's just a little less useful because I can't call the specific constructor if T is a non-primitive. As a compromise I do this:
(T)(value), but I'm probably getting the worst of both worlds.

[kbw]

Isn't the problem caused by returning a value rather than a ref? It you already have the thing stored, it should be a matter of just returning a reference to it?

Or maybe I just understand the context in which this is used.