Visual Basic Language Specification

8.3 Local Declaration Statements

A local declaration statement declares a new local variable. Its syntax is the same as a variable or constant declaration, except that a local variable declaration must always specify a modifier.

There are three kinds of locals. Regular locals are declared using the Dim modifier. Constant locals are equivalent to type-member constants and are specified with the Const modifier. Static locals are locals that retain their value across invocations of the method; static locals are declared using the Static modifier. Static locals declared within nonshared methods are per instance: each instance of the type that contains the method has its own copy of the Static local. Static locals declared within Shared methods are per type; there is only one copy of the Static local for all instances.

Variable initializers on locals are equivalent to assignment statements placed at the textual location of the declaration. Thus, if execution branches over the local declaration, the variable initializer will not be executed. If the local declaration is executed more than once, the variable initializer will be executed an equal number of times. It is important to note that locals are only initialized to their type's default value once, upon entry into the method.

Local variables are scoped to the statement block in which they are declared.

LocalDeclarationStatement ::= LocalModifier LocalDeclarator StatementTerminator

LocalModifier ::= Static | Dim | Const

LocalDeclarator ::=
LocalIdentifiers [ As TypeName ]
Identifier [ ArrayNameModifier ]
[ As [ New ] TypeName [ ( [ ArgumentList ] ) ] ] [ = VariableInitializer ]

LocalIdentifiers ::=
Identifier [ ArrayNameModifier ] |
LocalIdentifiers , Identifier [ ArrayNameModifier ]

LocalVariableName ::= Identifier

{
Int32 i;
i=1;
}

Int32 i;
Console.WriteLine(i);
i=1;

if (condition)
{
  char buffer[10000];
}

DG>if (condition)
DG>{
DG>  char buffer[10000];
DG>}
DG>

8:            if(true)
0040103B B9 01 00 00 00       mov         ecx,1
00401040 85 C9                test        ecx,ecx
00401042 74 07                je          main+3Bh (0040104b)
9:            {
10:               char buffer[10000];
11:               buffer[0] = 1;
00401044 C6 85 F0 D8 FF FF 01 mov         byte ptr [buffer],1

#define USES_DEBUG() WCHAR __buf_[1024];

_text:0044249F                 sub     esp, 8
_text:004424A2                 sub     esp, 8
_text:004424A5                 lea     ecx, [esp+0B8h+var_44]
_text:004424A9                 fstp    [esp+0B8h+var_B0]
_text:004424AD                 fsin
_text:004424AF                 fstp    [esp+0B8h+var_B8]
_text:004424B2                 call    sub_0_42C270

If you do not specify an initialization value for a variable, Visual Basic initializes it to the default value for its data type. The default initialization values are as follows:

0 for all numeric types (including Byte).
Binary 0 for Char.
Nothing for all reference types (including Object, String, and all arrays).
False for Boolean.
12:00 AM of January 1 of the year 1 for Date.
Each element of a structure or array is initialized as if it were a separate variable.