Initialization is a processing assigning an initial value to a variable while declaring it. For example,
int age = 12;When the compiler encounters this, it allocates the memory to the variable and assigns the value to it.
In c++ there are various ways to initialize variables, each of having their own quirks and benefits.
Forms of initialization in C++
There are 5 common forms.
int a; // default-initialization
// traditional initialization forms
int a = 1; // copy-initialization
int a (1); // direct-initialization
// modern initialization forms
int a {}; // value-initialization (or zero-initilization if garbage value is zero)
int a {1}; // direct-list-initializationcopy-initialization
Value on the right hand size is copied to the variable. This form is usually less efficient. However, in old code this form usually used as it easy to read.
direct-initialization
Initialization value is provided in paranthesis.
list-initialization
Curly braces are used for initialization. These forms are commonly used now a days. It also has two forms.
int a {3};
// and
int a = {3}; // copy-list-initializationcopy-list-initialization is rarely used.
Advantage of list-initialization is that it disallows narrowing conversions and violations of that leads to compile time errors or warning. For example,
int a {4.5}; // gives compile time error/warningHowever, reassigning value using copy-assignment later does narrowing conversions.
int a {4.5};
a = 5.5; // no issuesvalue-initialization
This form is used when no initial value is specified. In this case, variable will most likely to initialized to zero (or closet to zero). If zero is initialized, this is called zero-value-initialization.