C# & VB.NET Conversion Pocket Reference

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C# & VB.NET Conversion Pocket Reference

Imports System.Runtime.InteropServices

Sub MakeDeposit(<Out( )> ByRef num1 As Integer)

End Sub

This code declares the num1 parameter in MakeDeposit as an

out parameter. The C# version is simpler, since the lan-

guage provides a keyword that automatically adds the

attribute. However, placing the attribute in VB accomplishes

the same task. A drawback of the VB style is that the lan-

guage does not enforce the concept automatically. In C#, if

you mark a parameter as

out, the function must set the

parameter to a value before returning to the caller; other-

wise, the compiler generates an error. But in VB, you can

apply the attribute to a

ByRef parameter or to a ByVal param-

eter. The latter is a mistake, but the compiler does not

enforce the rule.

Passing Function Parameters

In C#, if a function contains ref parameters, you must use

the

ref keyword in front of each by reference argument when

you call it. The same is true for out parameters—the

out key-

word must appear before any argument that corresponds to

an out parameter. Also in C#, it is illegal to pass in a literal

value as an argument for a ref or out parameter. (You cannot

pass a number for a

ref int parameter, for example.) Any

variable you pass as a ref argument must be initialized before

making the method call. The following code segment illus-

trates these principles:

static void DoSomething(int x, ref int y,

out int z)

{

z=45;

}

static void Main(string[] args)

{

int y=4; //you must declare a variable

//and initialize it.

int z;

//notice the use of the ref and out

VB

C#

Syntax Differences

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//before each ref and out argument.

DoSomething(5,ref y,out z);

}

In VB, you do not use any keywords in front of the method

arguments, whether they are

ByVal, ByRef,or<Out> ByRef.

The example below shows how to call functions with

ByRef

parameters in VB.NET:

Imports System.Runtime.InteropServices

Module Module1

Sub DoSomething(ByVal x, ByRef y, <Out( )> ByRef z)

z = 45

End Sub

Sub Main( )

Dim y As Integer

Dim z As Integer

'y and z do not have to be

'initialized because VB auto

'initializes variables

DoSomething(5, y, z)

'it is also legal in VB.NET to

'pass literal values for ByRef

DoSomething(5, 10, 20)

End Sub

End Module

Notice that it is not necessary to use ByRef in front of the

ByRef arguments or to initialize argument variables, because

VB auto-initializes local variables. Notice too that VB lets

you send literal values for

ByRef parameters.

Inside the IL

Whenever you make a method call in VB.NET and you use

a literal value for a

ByRef parameter, at the IL level VB

declares a hidden local variable, assigns it the value you are

passing, and passes the address of the variable instead of the

literal value to the function.

VB