Using pointer as a template parameter

Question

In C++ I can do something like this:

template <typename T, T* Ptr>
class MyClass {};

I have two questions:

Where can I get a pointer other than nullptr in compile time?
How can I use this language feature? Of course, it would be interesting for practical cases, but it seems that this is a rather specific possibility, so an artificial example will also be suitable.

You can get a pointer to anything with static storage duration and linkage at compile time. — super
– super, Commented Jan 12, 2021 at 8:46

Jarod42 · Accepted Answer · 2021-01-12 09:08:03Z

3

You can get a pointer to anything with static storage duration and linkage at compile time:

static const int values[] = {4, 8, 15, 16, 23, 42};
MyClass <const int, values> myClass;

static char magic = '*';
MyClass <char, &magic> myClass2;

Demo

answered Jan 12, 2021 at 9:08

Jarod42

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5 Comments

dasfex Over a year ago

When it can be useful?

Jarod42 Over a year ago

Whereas you need constexpr pointer in template, might be useful to add name to template class. I already used it to serialize classes into Json.

yaodav Over a year ago

on option where it can be useful it in the embedded system where you have static memory maps for a different section - and it const.

dasfex Over a year ago

@Jarod42, what means "to add name to template class"? You can also use empty struct for that. Or maybe this is one from all solutions?

Jarod42 Over a year ago

It is one available tool. It (might) have alternative. Runtime pointer might also be enough. Can also be there in generic programming, so no special cases for pointers.

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