Ref And Out KeyWords - Two Separated Twins

Akbar Mulla

12 Comments

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Tarique Sultan8y ago
Sir I don't get your point in Last line which you explain in C# 7.O "From C# 7.0 onwards, there is no need to declare out parameter. It can be passed directly to the call method without declaration. Below is the code snippet for it." Kindly explain it ?
- Akbar Mulla8y ago
  Tarique, you can see in Line no.15 , the 3rd variable i.e. "out iOutVar2" is not declared and it has been driectly passed to the called function. This concept is new in C# 7.0. C# 7.0 came up with VS 2017. If you want the above code to work without error you should try in VS 2017. ;) :)
- Hadrian Tang8y ago
  I think he is trying to refetence the "out var" feature. However, the code failed to demonstrate it.
- Tarique Sultan8y ago
  May you are right but code is not working as for! He must rewrite article once!!
Bhavesh Jadav8y ago
Good...............
Satish Kumar Vadlavalli8y ago
I like your way of writing :)
Nicholas Tanvis8y ago
I noticed a typo at line 12 on the last code block. Shouldn't it be `int iRefVar = 20;`?
- Akbar Mulla8y ago
  Thanks Nicolas. Yes its a typo mistake. I will update it now. :)
Khaja Moizuddin8y ago
Great start..... Good one.
- Akbar Mulla8y ago
  Thanks................................ :)
Vishal Prajapati8y ago
Nice article..keep up the good work
- Akbar Mulla8y ago
  Thanks :) !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

In this article, I am going to explain the concepts of some useful keywords, like Ref & Out parameters. These keywords are used along with the data to be passed to a function as a parameter. Below, I will explain in brief about each of these keywords with an example.

Ref Keyword

The Ref keyword causes an argument of a function to be passed by reference and not by value. Any change made to the parameters in the called method will reflect its original value. For example, if you pass a local variable, and the call method changes the object to which the ref parameters refer, then the local variable now points to the new object; i.e., in simple words the value got updated to the new value.

It is mandatory to declare and assign a value to the variable which needs to get passed as a ref parameter. Otherwise, it will give a compilation error as below.

Programming Example 1: Using Ref Keyword

using System;
namespace RefOutParams {
class RefExample {
public void show(int iLocalVar, ref int iRefVar) {
iLocalVar += 10;
iRefVar += 10;
}
}
class Program {
static void Main(string[] args) {
int iLocalVar = 10, iRefVar = 10;
RefExample objRef = new RefExample();
objRef.show(iLocalVar, ref iRefVar);
Console.WriteLine(String.Format("Local Variable : {0}", iLocalVar));
Console.WriteLine(String.Format("Referenced Variable : {0}", iRefVar));
}
}
}

Output

Local Variable: 10
Referenced Variable: 20

Out Keyword

The Out keyword also causes an argument of a function to be passed by reference only. It is also the same as ref parameter, except that ref requires the variable to be initialized before it is passed to the method, while for out doesn't need initialization of the variable.

Programming Example 2: Using Out Keyword

using System;
namespace RefOutParams {
class OutExample {
public void show(ref int iRefVar, out int iLocalVar1, out int iLocalVar2) {
iRefVar += 10;
iLocalVar1 = 100;
iLocalVar2 = 200;
}
}
class Program {
static void Main(string[] args) {
int iRefVar = 20;
int iOutVar1 = 0, iOutVar2;
OutExample objOut = new OutExample();
objOut.show(ref iRefVar, out iOutVar1, out iOutVar2);
Console.WriteLine(String.Format("Referenced Variable: {0}", iRefVar));
Console.WriteLine(String.Format("Out Parameter Variable 1: {0}", iOutVar1));
Console.WriteLine(String.Format("Out Parameter Variable 2: {0}", iOutVar2));
}
}
}

Output

Referenced Variable: 30
Out Parameter Variable 1: 100
Out Parameter Variable 2: 200

Some points to remember while considering out parameter:

Out parameter should always be assigned a value in call method, otherwise it will throw a compilation error as shown below. In case of ref parameter, though the value is not assigned to it, it will not throw any compilation error. Have a look at the below image.

Out parameter should never be used to assign a value to any other variable as it will throw the compilation error. The reason behind this is that out parameters are allowed to be passed without initialization. Have a look at the below code where the parameter was initialized before getting passed to the method but still shows compilation error.

Note

From C# 7.0 onwards, there is no need to declare out parameter. It can be passed directly to the call method without declaration. Below is the code snippet for it.

Programming Example 3: Using Out Keyword in with C# 7.0

using System;
namespace RefOutParams {
class OutExample {
public void show(ref int iRefVar, out int iLocalVar1, out int iLocalVar2) {
iRefVar += 10;
iLocalVar1 = 100;
iLocalVar2 = 200;
}
}
class Program {
static void Main(string[] args) {
int iRefVar = 20;
int iOutVar1 = 0;
OutExample objOut = new OutExample();
objOut.show(ref iRefVar, out iOutVar1, out iOutVar2);
Console.WriteLine(String.Format("Referenced Variable: {0}", iRefVar));
Console.WriteLine(String.Format("Out Parameter Variable 1: {0}", iOutVar1));
Console.WriteLine(String.Format("Out Parameter Variable 2: {0}", iOutVar2));
}
}
}

Output

Referenced Variable: 30
Out Parameter Variable 1: 100
Out Parameter Variable 2: 200

Conclusion

Remember, it is mandatory to use ref & out while passing a value to a function. I hope you enjoyed the article.