Zero-reinitializing a struct in C++

Question

A POD struct can be zero-initialized in C++11 as follows:

SomeStruct s{}; 

However, what do I do if I already have an instance of the struct and I want to re-initialize it to zeros? The following seems to work:

s = {}; 

Can someone point out the relevant standardese? I assume this is what is happening:

1. A new zero-initialized instance gets created.
2. The new instance is assigned to the existing instance, invoking the implicit assignment operator.

Answer 1

What you are looking for is in [expr.ass]

A braced-init-list may appear on the right-hand side of

• an assignment to a scalar, in which case the initializer list shall have at most a single element. The meaning of x={v}, where T is the scalar type of the expression x, is that of x=T{v}. The meaning of x={} is x=T{}.
• an assignment to an object of class type, in which case the initializer list is passed as the argument to the assignment operator function selected by overload resolution (13.5.3, 13.3).

So your guess is correct. The compiler may (can in C++17 and above) be able to optimize things away but you can think of it as create a zero-initialized temporary and pass it to the operator=.