C# Out Parameter

Introduction to C# Out Parameter

‘out’ is a keyword in C#, which is used to pass arguments to a method as a reference type. Variables passed to a method as out parameters do not need to be declared or initialized before they are passed to the method call. The called method is required to assign values to the variables of out parameters before the control leaves the called method and before the called method returns any value to the calling method. It is possible to pass multiple out parameters to a method and the method returns multiple values.

Syntax with explanation:

While calling the method using the out parameter, the syntax will be as follows:

Method_name(out data_type variable_name);

Here, Method_name is any user-defined name given to the method, ‘out’ is the keyword used to express that the variable passed to the method is an out parameter, data_type can be any data type of the variable and variable_name is the user-defined name of the variable.

The syntax for the method to be called is as follows:

access_specifier return_type Method_name(out data_type variable_name);

Here, access_specifier can be any access specifier among the five access specifiers supported by C# like a public or private. Then, return_type is the type of data this method returns followed by method name and ‘out’ parameter list.

How ‘out’ parameter works in C#?

In C#, ‘out’ keyword works similar to the ‘ref’ and ‘in’ keywords. The difference between ‘out’ and ‘ref’ parameters is that, ‘out’ parameter variables do not need to be initialized before they are passed to a method, the user can declare the ‘out’ parameter variable in the argument list of the method instead of declaring it separately which is called inline declaration of ‘out’ parameter whereas the ‘ref’ parameter variables need to be initialized before they are passed to a method. The inline declared ‘out’ parameters can be accessed in the same block of code.

Example #1

Code:

using System;
namespace ConsoleApp4
{
public class Program
{
public static void Main(string[] args)
{
//inline declaration of 'out' parameter
Display(out int num);
Console.WriteLine("Value of variable 'num': {0}", num);
Console.ReadLine();
}
public static void Display(out int a)
{
//need to assign value
a = 10;
a += a;
}
}
}

Output:

• Now, the difference between ‘out’ and ‘in’ keyword is that, ‘out’ parameter values can be modified inside the called method whereas the ‘in’ parameter values cannot be modified inside the called method.
• A method can have more than one ‘out’ parameters such as: Display(out x, out y);
• To work with ‘out’ parameters, the user needs to explicitly use the ‘out’ keyword in the method definition and also in the calling method. At the same time, it is not necessary that the names given to the ‘out’ parameters in method definition and call should be the same.
• The ‘out’ parameters are passed by reference to a method therefore they do not create new storage location in the memory and uses the same storage location occupied by the variable arguments in the method invocation. As the method using ‘out,’ parameters can return multiple values, it helps the user to get multiple processed values from the called method. But before the method returns any value to the calling method, the ‘out’ parameters must be assigned with some values in the method.
• We cannot work with ‘out’ parameters in all types of methods like we cannot use ‘out’ parameters in asynchronous methods which we define using ‘async’ modifier and also we cannot use ‘out’ parameters in ‘iterator’ methods which consist of ‘yield return’ or ‘yield break’ statement. As properties are not variables, therefore, we cannot pass them as ‘out’ parameters to a method.
• The ‘out’ parameter can be defined using a generic type to indicate that the type parameter is covariant. Along with this the ‘out’ parameter is used in the TryParse() methods for different data types in C#. The TryParse() method returns a Boolean value which specifies success or failure and on the success, the result is given by the ‘out’ parameter.

Example #2

Code:

using System;
namespace ConsoleApp4
{
public class Program
{
public static void Main(string[] args)
{
string str = "123456";
int num;
//if ‘canParse’ is true; the result of conversion will be stored in ‘num’
bool canParse = Int32.TryParse(str, out num);
if (canParse)
Console.WriteLine(num);
else
Console.WriteLine("Could not be parsed.");
Console.ReadLine();
}
}
}

Output:

Examples of C# Out Parameter

Given below are the examples of C# Out Parameter:

Example #1

Example showing multiple ‘out’ parameters passed to a method and then the method returns multiple values.

Code:

using System;
namespace ConsoleApp4
{
public class Program
{
public static void Main()
{
//declaring variables without assigning values
float area, perimeter;
//passing multiple variables to a method using 'out' keyword
Calculate(5, 10, out area, out perimeter);
//displaying the result
Console.WriteLine("The area of rectangle is: {0}", area);
Console.WriteLine("The perimeter of rectangle is: {0}", perimeter);
Console.ReadLine();
}
//method taking length & breadth & it will return area and perimeter of rectangle
public static void Calculate(int length, int breadth, out float area, out float
perimeter)
{
area = length * breadth;
perimeter = 2 * (length + breadth);
}
}
}

Output:

Example #2

Example showing the inline declaration of ‘out’ parameter.

Code:

using System;
namespace ConsoleApp4
{
public class Program
{
public static void Main()
{
//in-line declaration of variables without assigning values
Calculate(out int length, out int breadth, out float area);
//displaying the values of length, breadth, and area
Console.WriteLine("Length of rectangle: " + length);
Console.WriteLine("Breadth of rectangle: " + breadth);
Console.WriteLine("Area of rectangle: " + area);
Console.ReadLine();
}
//method taking 'out' parameters and it returns multiple values
public static void Calculate(out int l, out int b, out float a)
{
l = 30;
b = 40;
a = l * b;
}
}
}

Output:

Conclusion

‘out’ parameter in C# allows users to pass arguments by reference to a method. Variable used as ‘out’ parameter does not require to be initialized before it is passed to a method. The called method should assign value to the out parameter before it returns a value.

This is a guide to the C# Out Parameter. Here we discuss the introduction, examples and how ‘out’ parameter works in C#? You may also have a look at the following articles to learn more –

1. Overloading and Overriding in C#
2. Constructor in C#
3. Polymorphism in C#
4. Math Functions in C#