This document provides difference between Ref and Out Parameters

1. Difference between Ref and Out parameters
S.No Ref Out
1 Ref parameters are both input and Out parameters are only for output - a
output - a value is passed into a value is passed out of a method
method and a new value is passed
out
2 An argument passed to ref out argument does not have to be
parameter must be initialized explicitly initialized.
3 Ref parameter may be written to Out parameter must be written to
before returning from method before returning from method
4 Ref parameter may be referenced Out parameter may not be referenced
inside method before being inside method before being written to
written to
Example for ref parameter :
class Program
{
static void M1(ref int i)
{
i = 1;
i += 1;
}
static void Main(string[] args)
{
int j=0; //Assigned
M1(ref j);
Console.Write(j);
Console.Read();
}
}
The output is same: 2, but we have to assign the variable before used otherwise we will get an error.
Example for out parameter :
class Program
{
static void M1(out int i)
{
i = 1;
i += 1;
}
static void Main(string[] args)
{

2. int j; //Not assigned
M1(out j);
Console.Write(j);
Console.Read();
}
}
}
The output is : 2
Summary:
1. Both are treated differently @ runtime but same in the compile time, so can’t be overloaded.
2. Both are passed by references except ‘ref’ requires that the variable to be initialized before
passed.
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