What are initializer lists in C++?
Educative Answers TeamThe initializer list is used to directly initialize data members of a class. An initializer list starts after the constructor name and its parameters. The list begins with a colon ( : ) and is followed by the list of variables that are to be initialized – all of the variables are separated by a comma with their values in curly brackets.
Syntax
Constructorname(datatype value1, datatype value2):datamember(value1),datamember(value2)
{
...
}
Using an initialization list is almost identical to doing direct initialization (or uniform initialization in C++11).
Code
The following example uses an initializer list in the default constructor to set the value for the variable value of the class.
#include<iostream>
using namespace std;
class Base
{
private:
int value;
public:
// default constructor
Base(int v):value(v)
{
cout << "Value is " << value;
}
};
int main()
{
Base myobject(10);
return 0;
}There are several cases where the use of an initializer list is absolutely necessary, these include:
1. Initializing a reference type data member
An initialization list is used to initialize a data member of reference type. Reference types can only be initialized once.
#include<iostream>
using namespace std;
class Base
{
private:
int &ref;
public:
Base(int &passed):ref(passed)
{
cout << "Value is " << ref;
}
};
int main()
{
int ref=10;
Base myobject(ref);
return 0;
}2. Initializing const data member
const data members can be initialized only once, so they must be initialized in the initialization list.
#include<iostream>
using namespace std;
class Base
{
private:
const int var;
public:
Base(int constant_value):var(constant_value)
{
cout << "Value is " << var;
}
};
int main()
{
Base myobject(10);
}3. Initializing member objects which do not have a default constructor
If you have a field that has no default constructor (or a parent class with no default constructor), then you must specify which constructor you wish to use.
#include<iostream>
using namespace std;
class Base_
{
public:
Base_(int x)
{
cout << "Base Class Constructor. Value is: " << x << endl;
}
};
class InitilizerList_:public Base_
{
public:
// default constructor using initializer list
InitilizerList_():Base_(10)
{
cout << "InitilizerList_'s Constructor" << endl;
}
};
int main()
{
InitilizerList_ mylist;
return 0;
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