Advantages of using initializer list? [duplicate]

Answer 1

If you don't use the initializer list, the member or base class gets default constructed before the opening curly brace.

So, your calls to set it later will add an operator=() call.

If you use the initializer list, the member or base class has the proper constructor called.

Depending on your classes, this might be required or faster.

Answer 2

Also, never perform unmanaged resource acquisition in initializer lists. In other words, either use "resource acquisition is initialization" (thereby avoiding unmanaged resources entirely) or else perform the resource acquisition in the constructor body.

And warning #2 Perform every resource allocation (e.g., new) in its own code statement which immediately gives the new resource to a manager object (e.g., auto_ptr).

http://www.gotw.ca/gotw/056.htm

Answer 3

For primitives, there is no difference between using initializer lists or constructing them via assignment.

For other types, initializer lists might afford you performance improvements when constructing objects.

Do note that the order of initializing (in initializer lists) depends on the order of declaration in the class. If the declarations are out of order and you need to construct data that depends on something else already being initialized before hand, that is an exception to the 'use initialization lists when possible rule'.

More info: http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.6

Answer 4

other than being forced to use an initializer list for constants and references, It also useful because with it you avoid default constructing member objects before the constructor is entered and then immediately assigning it, which can be inefficient if the member objects are expensive to construct

Answer 5

Apart from what everyone else has mentioned, it allows disambiguation of shadow variable, so where would have to write this->var = var you can instead do myclass(int var) : var(var). Of course some people might find this very confusing/hard to read if you have a big constructor