In Value initialization the initializer is an empty pair of parenthesis.
This is the major feature release in C++3.0
- If user has default Constructor – it calls constructor
- else, you get zero initialization.
example:
Case 1: Zero initialization
int main()
{
return int(); // value initialization
}
Case 2: No user defined constructor i.e. no user defined initialization.
struct Foo
{
int i;
}
Foo get_foo()
{
return Foo();
}
int main()
{
return get_foo().i; //return 0.
}
Case 3: With User defined constructor
struct Foo
{
Foo() {} // constructor defined
int i;
}
Foo get_foo()
{
return Foo();
}
int main()
{
return get_foo().i; //Undefined behavior.
}Solution: defined constructor as default, which will return zero, as default signifies no user defined initialization.
Foo() = default;
Case 4: default constructor outside class, it will be treated as user provided.
struct Foo
{
int i;
}
Foo::Foo()=default; // constructor defined
Foo get_foo() {
return Foo();
}
int main()
{
return get_foo().i; //Undefined behavior.
}
