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What is the difference between ref and out keywords in method parameters?

Anubhav Sharma 462 10 Jun 2025

What is the difference between ref and out keywords in method parameters?

c# c#
Updated 12 Jun 2025
Anubhav Sharma
Anubhav Sharma

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The Anubhav portal was launched in March 2015 at the behest of the Hon'ble Prime Minister for retiring government officials to leave a record of their experiences while in Govt service .

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1 Answers

Ravi Vishwakarma
Ravi Vishwakarma 12 Jun 2025
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In C#, both ref and out are used to pass arguments by reference to a method, but they differ in terms of initialization requirements and intended purpose.

Key Differences

Feature ref out
Initialization before call ✅ Must be initialized ❌ Doesn't have to be initialized
Must be assigned in method ❌ Not required (but allowed) ✅ Must be assigned before return
Purpose Pass value in and out Return additional output from method
Common use Modify an existing variable Return multiple values

ref Example

void Update(ref int number)
{
    number += 10;
}

int x = 5;
Update(ref x);  // x becomes 15
  • Must initialize x before passing
  • Can read and write x inside the method

out Example

void GetValues(out int a, out int b)
{
    a = 10;
    b = 20;
}

int x, y;
GetValues(out x, out y);  // x = 10, y = 20
  • x and y don’t need initialization before the call
  • They must be assigned inside the method

Compile-Time Rules

Check ref out
Must be assigned before method ✅ ❌
Must be assigned in method ❌ ✅
Must use keyword when calling ✅ ✅

When to Use What?

Use Case Recommended
Modify input and return value ref
Return multiple values from a method out
Passing large structs efficiently ref

Bonus: ref readonly

You can also use ref readonly to pass by reference without allowing modification.

void PrintValue(ref readonly int value)
{
    Console.WriteLine(value);
}
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