C# out parameter
Description
An out argument is like a ref argument, except it:
- Variables need not be assigned before going into the function
- Parameters must be assigned before it comes out of the function
The out modifier is most commonly used to get multiple return values back from a method.
Syntax
out parameter has the following syntax:
methodName(out type parameter);
when calling the method
methodName(out variableName);Example
For example:
using System;//from w ww . j a v a 2s. c o m
class Point
{
public Point(int x, int y)
{
this.x = x;
this.y = y;
}
public void GetPoint(out int x, out int y)
{
x = this.x;
y = this.y;
}
int x;
int y;
}
class MainClass
{
public static void Main()
{
Point myPoint = new Point(10, 15);
int x;
int y;
myPoint.GetPoint(out x, out y);
Console.WriteLine("myPoint({0}, {1})", x, y);
}
}
The code above generates the following result.
Example 2
using System;/*from ww w . j a v a 2 s .c o m*/
class MyClass
{
public int Val = 20;
}
class MainClass
{
static void MyMethod(out MyClass f1, out int f2)
{
f1 = new MyClass();
f1.Val = 25;
f2 = 15;
}
static void Main()
{
MyClass myObject = null;
int intValue;
MyMethod(out myObject, out intValue);
Console.WriteLine("After -- myObject.Val: {0}, intValue: {1}", myObject.Val, intValue);
}
}
The code above generates the following result.
Note
Like a ref parameter, an out parameter is passed by reference.
When you pass an argument by reference, you alias the storage location of an existing variable rather than create a new storage location.
In the following example, the variables x and y represent the same instance:
using System;//from w w w . j av a 2 s. c o m
class MainClass
{
static int x;
static void Main() { Foo (out x); }
static void Foo (out int y)
{
Console.WriteLine (x); // x is 0
y = 1; // Mutate y
Console.WriteLine (x); // x is 1
}
}
The code above generates the following result.
