Identifiers by George Hernandez

Naming Restrictions
Variable Scope
Array Variables
Coding Conventions
Naming Conventions

Naming Restrictions

Identifiers must begin with a letter.
Identifiers can't contain embedded period or type-declaration character.
Identifiers can't be longer than 255 characters.
Identifiers can't be restricted keywords. EG: If.
Identifiers of controls, forms, classes and modules can't be longer than 40 characters.
Variable names must be unique within its scope.

Variable Scope

	Where Declaration Keyword Used (Scope & Lifetime)
Declaration Keyword	In Procedure of Any Module	In Declaration Section of Non-Standard Module	In Declaration Section of Standard Module (`.bas`)
Dim	Procedure & Procedure	Module & Application	Module & Application
Static	Procedure & Application	NA	NA
Private	Procedure & Procedure	Module & Application	Module & Application
Public	NA	Global & Application	Global & Application
Const	Global & Application	Global & Application	Global & Application

A variable, constant, or object variable is usually declared before using it. Explicit variable declaration is not required but highly recommended. For one, it helps Visual Basic spell check your variables. If using it be sure to use the Option Explicit keyword in the Declarations section of the module's code. Syntax:

{Dim | Static | Private | Public} Variable [As DataType]

{Dim | Static | Private | Public} Const Constant [As DataType] = expression

{Dim | ReDim | Static | Private | Public} ObjectVariable As [New] ClassOrObjeccodeype
...
Set <ObjectVariable> = [New] Object

Intrinsic or system defined constants are defined by the object library of the application or control.
Local variables shadow less local variables, i.e. the local folks are preferably accessed. To utilize public variables that have the same name but come from different modules, qualify the name with the module name. EG: Module1.strAge and Form1.strAge.
The Static keyword is either used within a procedure or at procedure declaration (to make all the variables in the procedure static). Static variables have procedure scope and application lifetime. This sounds like you might as well make a module or global scope variable but those variables would not be exclusive to the procedure.
Declare the data type of variables and constants by using the As keyword when declaring. If no data type is declared, Visual Basic will assume that the data type is variant. EG: The statement Dim Alpha, Beta As Byte, makes a variable called Alpha of the data type Variant and a variable called Beta of the type Byte.
To make fixed-length strings that pads with trailing spaces if necessary, use As String * n, where n is the desired length.
Do not declare global variables in class modules because a class module can make multiple object instances of itself, each with its own erroneously created global variable. It works but it violates object oriented programming concepts of encapsulation.
After declaring an object variable it can be set at some point in the module using the Set keyword. Note that you cannot use the New keyword with generic object types, fundamental data types (EG: Integer), specific control types (EG: TextBox), or specific controls (EG: TextBox1).

Array Variables

Declare arrays as you would a variable but with these modifications:

The upper bound in parenthesis. EG:

Dim intArray(3) As Integer
'VB6/VBS arrays are zero-based 'This array has 4 elements

The lower and upper bounds in parentheses if you don't want an array starting at 0. EG:
```
Private intArray(1 to 7) As String
```
Make an array of arrays by assigning each array to another array's index. An array can contain only one data type. However, it is possible to have a variant array can contain different arrays, each of which is of a different data type. EG:
```
Dim vntArrays(2) As Variant
Dim strArray(4) As String
Dim intArray(5) As Integer
vntArrays(0) = strArray
vntArrays(1) =  intArray
```
Make a multidimensional array by setting the bound(s) of the dimensions in parentheses separated by commas. EG:
```
Static bytMatrix(3, 1 to 7) As Byte
'VB6/VBS supports up to 60 dimensions
```

Nested For loops are great for processing multidimensional arrays. EG:

For I = 1 To 5
  For J = 1 To 10
    intMatrixA(I, J) = I * 10 + J
  Next J
Next I

For a dynamic array that can resize the bounds (but not the dimensions), first declare the array without bounds. EG:

Public myArray()

'and then (within a procedure only) 'use the ReDim keyword to set the variable size: 
ReDim my Array(x +1)

The ReDim keyword eliminates all data in the array before resizing. To preserve the data, the Preserve keyword must be used and only the upper bound can be resized. EG:
```
ReDim Preserve Array(UBound(Array)+1).
```
You may also create an array by using the VB function Array(argList). The function takes a comma delimited list of n values and return a variant array of size n. EG:
```
Dim A, B, C
A = Array(11,22,33)
B = A(2) 'B is now 22
C = Array() 'C is an array of zero length
```

Coding Conventions

See also Conventions.
A long statement can be broken into several lines by including a space and underscore ( _) at the end of each line.
One statement per line is standard. Multiple statements can be put on the same line if a colon (:) is placed between statements.
Use ampersand (&) to link strings and use plus sign (+) to link numerical values.
Visual Basic prefixes octal numbers with &O and hexadecimal numbers with &H. EG: 15 = &O17 = &HF.
Using the Option Explicit keywords at the start of each code module should almost be mandatory. It enables VB to check for errors on your identifiers.

Naming Conventions

See also Conventions.
Use upper case at the start of each word within the name. EG: DogBite. (Java and JavaScript folks like to capitalize only the second word and beyond. EG: dogBite.)
Use complete word whenever possible since abbreviations can vary, eg use PromotionalPrograms instead of ProPrg.
Use either verb/object or object/verb order when naming methods, eg DogRun and DogBite.
Multiple variables that have the same name can be qualified with their parent module name, eg Form1.Temp.
Intrinsic constants usually have a two character prefix indicating its originating library, eg vbTileVertical.
- Standard Visual Basic Constants prefixed with "vb". EG: vbCrLf.
- Standard ADO constants prefix with "ad". EG: adStatusOK.
- Intrinsic constants can also be qualified with this syntax: [LibraryName.][ModuleName.]ConstantName.
Use three character prefixes for Controls and objects. EG: Use imgDog and lblDog for the Dog image and label.
For prefixes to the intrinsic controls and common ActiveX controls, see Controls.
Prefix menu items with the name of the menu. EG: mnuFileSave or mnuFile_Save.
For menu items that need additional info from the user, the caption should be followed by ellipsis (...).

Here are common objects that may have some variation in multiple object models:

Prefix	Object	Prefix	Object
pnl acd ado ani cbr chk cht cbo cmd dlg or cdg cmg cnn cnt ctl cbr <user-defined> dat or dc dbs or db de or den drr dr or rpt dbe dir doc drv dtp edt err fil fso fra fld frm frs fra fsb grd grc grh flx hsb hpl img icb ilt idx itx	3D Panel ActiveDoc ADODataControl AnimatedButton/Animation CoolBar CheckBox Chart ComboBox/DBCombo/DataCombo CommandButton Common Dialog CommandGroup Connection Container Control CoolBar Custom Data Database DataEnvironment DataRepeater DataReport DBEngine DirListBox Document Drive/DriveListBox DatePicker EditBox Error FileListBox FileSystemObject Frame Field Form/MDIForm FormSet Frame FlatScrollBar Grid/DBGrid/DataGrid GridColumn GridHeader MSFlexGrid/MSHFlexGrid HScrollBar HyperLink Image ImageCombo ImageList Index InternetTransfer	lbl lin lst lvw map mbx mci mnu mvw obj olb ole opt opg pag pgf prm pic or pbx pbr prj ppy qrf rdc rst or rs rel rtf or rbx sep shp sld spn sbr sys tdg tbl tab txt or tbx tmr tbr tvw udn usr vsb wsk wsp	Label Line ListBox/DBList/DataList ListView MAPIMessages/MAPISession MaskedEditBox MultimediaMCI Menu MonthView Object OLEBoundControl OLE OptionButton OptionGroup Page PageFrame Parameter PictureBox ProgressBar ProjectHook Property QueryDef RemoteData Recordset Relation RichTextBox Separator Shape Slider Spinner StatusBar SysInfo TabbedDialog TableDef TabStrip TextBox Timer ToolBar TreeView UpDown User VerticalScrollBar WinSock Workspace

Page Modified: (Hand noted: 2007-09-20 20:02:00Z) (Auto noted: 2007-11-17 06:37:27Z)