Initialization in C++

Question

What is the difference between direct initialization and uniform initialization in C++?

What is the difference between writing

int a{5}; // Uniform

and

int a(5); // Direct

Answer 1

In this particular example there will be no difference due to the type and the value choosen: int and 5.

In some other cases what initialization means does depend on whether we use {} or (). When we use parenthesis, we're saying that the values we supply are to be used to construct the object, making a computation. When we use curly braces, we're saying that (if possible) we want to list initialize the object; If it is not possible to list initialize the object, the object will be initialized by other means.

E.g.

// a has one element, string "foo"
vector<string> a{"foo"};
// error, cannot construct a vector from a string literal
vector<string> b("foo");
// c has 21 default initialized elements
vector<string> c{21};
// d has 21 elements with value "foo"
vector<string> d{21, "foo"};

For a built-in type, such as int, the {} will have another function:

double d = 3.14;
int i = 0;
i = {d};
// error: narrowing conversion of ‘d’ from ‘double’ to ‘int’

For more information you may check the cppreference.com - Initialization