Initialization in C++

Initialization in C++ is important for writing efficient programs free from errors, as uninitialized variables can lead to unpredictable behavior and safety issues. C++ provides you with various types of initialization to optimize the codes and improve the performance. In this article, we will discuss initialization and initializer in C++, types of initialization, the difference between copy and direct initialization, and best practices for initialization.

Table of Contents:

• What is Initializer and Initialization in C++?
• Types of Initialization in C++
  • Zero Initialization
  • Default Initialization
  • Value Initialization
  • Copy Initialization
  • Direct Initialization
  • List Initialization
  • Member Initializer List
• Copy Initialization vs Direct Initialization in C++
• Static vs Dynamic Initialization in C++
• Best Practices for Initialization in C++
• Conclusion

What is Initializer and Initialization in C++?

An initializer in C++ is a value or an expression that can be used to set the initial state of a variable or an object at the time it is created. 

Initialization in C++ is the process of assigning an initial value to a variable or an object when it is created. Proper initialization in C++ makes sure that the variables have well-defined values before they are used in the program to avoid undefined behavior.

Example:

Output:

The above code shows how the different types of initialization in C++: copy, direct, and list initialization as a class Example is defined that uses a member initializer list to initialize a and then initializes and prints the primitive variables (num, pi) and an object(obj).

Types of Initialization in C++

There are various types of initialization in C++ that can occur at different stages in the program execution. Below, you will find a brief description of all the types by which you can initialize the variables and objects.

1. Zero Initialization

Zero initialization in C++ is used to set the variables to zero(0), nullptr, or false when they are declared. It can be applied to:

• Global and static variables, as this is their default behavior.
• Value initialization with { } or ( ) will ensure the zero initialization.
• Class members are zero-initialized if they are explicitly requested.

Example:

Output:

The code shows zero-initialization in C++ as the global and static variables are automatically initialized to 0, while the local variables and class members are initialized with { } and also get the default values.

2. Default Initialization

Default initialization in C++ occurs when a variable is declared without an explicit initializer. The behavior of default initialization depends on the types of variables and storage class:

• Local variables are uninitialized and can contain garbage values.
• Global and static variables are zero-initialized by default.
• Class members are uninitialized unless they are explicitly initialized.
• Static class members are automatically set to zero.
• Objects of user-defined data types call the default constructor if it is available.

Example:

Output:

The code shows how the default initialization works in a C++ program, as the variables and class members of int and double are not assigned any value, so obj.x and obj.y remain uninitialized and may contain garbage values, which lead to unexpected behavior.

3. Value Initialization

Value initialization in C++ makes sure that the variable is given a well-defined initial value. It can be applied when a variable is initialized using the empty { } or ( ) without arguments:

• Built-in types such as int and float are zero-initialized.
• Class types call the constructor if available.
• Dynamically allocated objects are also zero-initialized when using the new T( ).

Example:

Output:

The code shows how the value initialization works in C++, as here a, b, and all members of obj are initialized with the value zero.

4. Copy Initialization

Copy initialization in C++ is a way of initializing a variable using the = operator. It calls the copy constructor for the objects or performs an implicit conversion if it’s necessary. Copy initialization is commonly used for initializing the variables with the values of the same or compatible types. It occurs in the following cases:

• When a variable is initialized with the = operator.
• Passing arguments to a function by value.
• Returning a value from a function.
• When the class objects are initialized using the = operator.
• When an object is copied to another object.
• Initializing the standard conversions with the = operator. 

Example:

Output:

The code shows how the copy initialization works in C++ as the integer a is initialized with the value 10, and the obj is initialized with the value 20 by calling the constructor Example, and then the constructor assigns the value 20 to the obj. Value that will be printed as an output.

 5. Direct Initialization

Direct initialization in C++ occurs when a variable or an object is initialized using the parentheses ( ) instead of the = operator. It is commonly used for class objects and primitive types and helps to restrict implicit conversions in some cases. It occurs in the following cases:

• When the variables are initialized with the parentheses ( ).
• Calling a constructor explicitly for the class objects.
• Passing an argument to function parameters by value.
• Returning an object from a function.
• When the standard library containers are initialized.
• When a memory is allocated using the new operator with initialization.

Example:

Output:

The code shows how the direct initialization works in a C++ program as the integer a is directly initialized with the value of 10 and the obj is directly initialized with the value of 50 by calling the Example constructor, and then the constructor assigns the value 50 to obj. Value, so the output is 50.

6. List Initialization

List Initialization in C++ uses curly braces { } to initialize the variables and objects. It is also called as the uniform initialization. It is introduced in C++11, mostly helps to prevent narrowing conversions, and provides a consistent syntax across different types. It can be used in the following cases:

• For initializing the primitive data types, class objects, standard library containers, arrays, structs, and aggregate types.
• For the constructor initialization in the classes.
• To avoid the narrowing conversions.
• It can be used for dynamic memory allocation.

Example:

Output:

The code shows how the list initialization works in a C++ program using the { } syntax as it initializes int a with 10,  double b with 3.14, and v with the elements 1, 2, 3, 4, and 5, and then the output is printed.

7. Member Initializer List

A member initializer list in C++ is used in a class constructor to initialize the member variables before the constructor body is executed. It makes sure of the direct initialization of members, improves performance, and allows the initialization of the const and the reference members.

Example:

Output:

The code shows how the member initializer list works in a C++ program. As in the above code, the value is initialized directly in the constructor since it is more efficient than assigning the value inside the constructor body, and then Value: 10 is printed to the console.

Copy Initialization vs Direct Initialization in C++

Static vs Dynamic Initialization in C++

Best Practices for Initialization in C++

1. You should initialize the variables because uninitialized variables will lead to undefined behavior and errors.
2. Always use the direct initialization, as it is more efficient than copy initialization and helps prevent unnecessary copies.
3. You must use the member initializer list for the class members, as it provides efficient initialization for the const and the reference members. 
4. Always initialize the static and global variables properly, as these are zero-initialized by default. 
5. You should use the uniform initialization { } wherever it is possible to avoid the narrowing conversions.
6. You should avoid the initialization in the loops when it is unnecessary because it can reduce the performance.
7. You can use the constexpr or const for the constant values to help the compiler optimize the code and prevent unintended changes.

Conclusion

Initialization in C++ is an important task in C++ programs as it makes sure that the variables and the objects start with well-defined values. As we have discussed above in C++, various types of initialization help you to avoid unexpected errors in the coding and also improve the performance and code clarity. So, by understanding the initialization and its types with the best practices, you can write reliable and efficient C++ programs.

FAQs on Initialization in C++