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

Question

ICSM Computer · Answer

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 passingCan 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 callThey 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);
}

forum

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

Anubhav Kumar

Can you answer this question?

1 Answers

Key Differences

`ref` Example

`out` Example

Compile-Time Rules

When to Use What?

Bonus: `ref readonly`

Liked By

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

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

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