Unified Initialization with {}

The initialization of variables became uniform in C++11. For unified initialization, we need the {} brackets.

{} initialization is always applicable.

Direct initialization #

Variables can be declared directly without the assignment operator:

std::string str{"my String"};
int i{2011};

Copy initialization #

{} also supports copy initialization with the = operator:

std::string str = {"my String"};
int i = {2011};

The difference is that direct initialization directly calls the constructor of the type, whereas, in copy initialization, the value is created and implicitly converted into the type.

Preventing narrowing #

Narrowing, or more precisely narrowing conversion, is an implicit conversion of arithmetic values from one type to another. This can cause a loss of accuracy, which can be extremely dangerous.

The following example shows the issue with the classical way of initializing fundamental types.

The compiler presents a warning, yet the implicit conversions are performed nonetheless, resulting in data loss.

It doesn’t matter whether we use direct initialization or assignment: