Initialize array based on C++ version and compiler

Question

In C++11 or higher regardless of compiler int myArray[10] = { 0 }; would initialize to all elements to zero. The question is would this also work in C++98 and could the compiler not decide to initialize all elements to zero? In other words could C++98 with a given compiler ignore the assigning zero to all elements?

I found this page: https://en.cppreference.com/w/cpp/language/zero_initialization which lists C++98 defects about zero initialization.

I guess this could be a duplicate: c++ array initialization, the accepted answer has a quote from standard. But a good answer here could also be welcome. — Yksisarvinen
– Yksisarvinen, Commented May 13, 2022 at 21:40
I don't see where you get the supposed different C++98 behavior from. Cppreference also clearly states that pre-C++11 the remaining elements are value-initialized, meaning for int zero-initialized. See en.cppreference.com/w/cpp/language/aggregate_initialization. — user17732522
– user17732522, Commented May 13, 2022 at 21:54
The defect reports listed on the linked page all seem irrelevant to the example. — user17732522
– user17732522, Commented May 13, 2022 at 21:58
@user4581301 - I enjoy the implementation, since it most closely matches how we do things without computers. string employees[10] = {"me", "son"}. Cool - there's room for 10 employees and we know the names of 2 of them. Should we initialize the other 8 positions to a copy of either of the first two, or something else. Why? That's my justification for why such behaviour can be the only reasonable one. — enhzflep
– enhzflep, Commented May 13, 2022 at 21:58
@user17732522 The defect is that in C++98, value initialization was not a thing. See: stackoverflow.com/questions/27349679/… — NathanOliver
– NathanOliver, Commented May 13, 2022 at 22:24

eerorika · Accepted Answer · 2022-05-13 22:37:16Z

All elements would be zero. Quotes from C++98:

[dcl.init.aggr]

If there are fewer initializers in the list than there are members in the aggregate, then each member not explicitly initialized shall be default-initialized (8.5)

[dcl.init]

To default-initialize an object of type T means:

if T is a non-POD class type (clause 9), the default constructor for T is called (and the initialization is ill-formed if T has no accessible default constructor);

if T is an array type, each element is default-initialized;

otherwise, the storage for the object is zero-initialized.

The meaning of default initialisation was radically different in C++98 compared to its meaning starting from C++03 where the old default initialisation essentially was renamed value initialisation and the new default initialisation became to mean "no initialisation" for trivial types.

Note that int myArray[10] = {}; would achieve the same goal. It's unnecessary to explicitly provide a value for the first element.

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