What is the difference between "ref" and "out" keywords?
- By default, the parameters are passed to a method by the value.
- By using ref and out, we can pass a parameter by reference.
The ref Modifier
- Used to state that the parameter passed may be modified by the method.
- It is necessary the parameters should initialize before it passes to ref.
- Useful when the called method also needs to change the value of a passed parameter.
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
int id = 1;
Console.WriteLine("id = " + id.ToString()); // id = 1
string newString = GetString(ref id);
Console.WriteLine("id = " + id.ToString()); // id = 2
}
public static string GetString(ref int id)
{
id += 1;
return "String";
}
}
The out Modifier
- Used to state that the parameter passed must be modified by the method.
- It is not necessary to initialize parameters before they pass to an out.
- Useful when a method returns multiple values.
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
int id =1;
Console.WriteLine("id = " + id.ToString()); // id = 1
string newString = GetString(out id);
Console.WriteLine("id = " + id.ToString()); // id = 2
}
public static string GetString(out int id)
{
id = 2;
return "String";
}
}
Note: Both ref and out parameters are treated the same at compile-time but different at run-time.
| ref |
out |
| The parameter or argument must be initialized first before it is passed to the ref |
Not required to initialize the parameter or argument before passing it to an out |
| Not required to assign or initialize the value of a parameter before returning to the calling method. |
A called method is required to assign or initialize a value of a parameter before returning to the calling method. |
| Data can be passed bi-directionally |
Data is passed only unidirectional way ( from the called method to the caller method) |
| Useful when the called method is also needed to modify the passed parameter |
Useful when multiple values need to be returned from a function or method. |