Is this code legal in ISO C++? - c++

Question

So I'm trying to implement function parameters which can be uninitialized. Here is the code which I have written. My question is if it's legal by the ISO C++ standard (version 14 if possible).
#include <iostream>
#include <typeinfo>
using namespace std;
template<typename type>
struct nzeroinittmpliteral
{
nzeroinittmpliteral() { }
nzeroinittmpliteral(type arg) { d = arg; }
//nzeroinittmpliteral(const nzeroinittmpliteral &) = delete;
operator type () & { return d; }
operator type () && { return d; }
type d;
} ;
void func(bool bIsPointerValid, nzeroinittmpliteral<int *> pVar = {})
{
if(bIsPointerValid)
{
cout << *pVar << endl;
}
else
{
pVar = new int;
*pVar = 8;
cout << *pVar << endl;
delete pVar;
}
}
int main()
{
func(true, { (int *)&(const int &)int{9} } );
func(false);
}

Answer 1

If you want to pass a parameter that may be uninitialized, simply don't pass it, use overloading. Look:
void func(int value)
{
cout << value << endl;
}
void func()
{
// no 'value' was initialized here :)
func(8);
}
Or simply give a default value to the parameter if you will provide one anyway in your body:
void func(int value = 8)
{
cout << value << endl;
}
Besides that, you can take a look at boost::optional:
void func(boost::optional<int> optvalue = boost::none) {
if (optvalue) {
cout << *optvalue << endl;
} else {
// nothing passed
cout << "foo" << endl;
}
}
Directly answering your question: your code is valid.
func(true, { (int *)&(const int &)int{9} } );
By casting the temporary to a const reference, you extend its lifetime to the lifetime of the reference itself, which ends after func returns. But this is too redundant, you could simply have written:
void func(int* value) { if (value) {...} }
func(&(const int &)9);
func(nullptr);
The actual parameter being passed is your nzeroinittmpliteral and it is initialized by calling one of the constructors, always. The default constructor doesn't initialize the d member, but this is no big improvement as it is just a pointer. Using nullptr is better and removes the need for the bool parameter.