Declare Statement

Description

Used at module level to declare references to external procedures in a dynamic-link library (DLL) or Macintosh code resource.

Syntax 1

[Public | Private ] Declare Sub name [CDecl] Lib "libname" [Alias "aliasname" ][([arglist])]

Syntax 2

[Public | Private ] Declare Function name [CDecl] Lib "libname" [Alias "aliasname" ] [([arglist])][As type]

The Declare statement syntax has these parts:

Part	Description

Public	Used to declare procedures that are available to all other procedures in all modules.
Private	Used to declare procedures that are available only within the module where the declaration is made.
Sub	Indicates that the procedure doesn't return a value.
Function	Indicates that the procedure returns a value that can be used in an expression.
name	Any valid procedure name.
CDecl	For the Macintosh only. Indicates that the procedure uses C language argument order, naming conventions, and calling conventions.
Lib	Indicates that a DLL or code resource contains the procedure being declared. The Lib clause is required for all declarations.
libname	Name of the DLL or code resource that contains the declared procedure.
Alias	Indicates that the procedure being called has another name in the DLL or is in a Macintosh code resource. This is useful when the external procedure name is the same as a keyword. You can also use Alias when a DLL procedure has the same name as a Public variable or constant or any other procedure in the same scope. Alias is also useful if any characters in the DLL procedure name aren't allowed in names.
aliasname	Name of the procedure in the DLL or code resource.
	In Microsoft Windows, if the first character is not a #, aliasname is the name of the procedure's entry point in the DLL. If # is the first character, all characters that follow must indicate the ordinal number of the procedure's entry point.
	On the Macintosh, the syntax to specify the code resource type is as follows:
	"[resourcetype]$[resourcename]"
	The resourcetype is any valid 4-character constant. If omitted, the default resourcetype is CODE. The resourcename is the procedure name in the code resource. If resourcename is omitted, it is assumed to be the same as name.
arglist	List of variables representing arguments that are passed to the procedure when it is called.
type	Data type of the value returned by a Function procedure; may be Boolean, Integer, Long, Currency, Single, Double, Date, String (variable length only), Object, Variant, a user-defined type, or an object type.

The arglist argument has the following syntax and parts:

[Optional][ByVal | ByRef][ParamArray] varname[( )][As type]

Part	Description

Optional	Indicates that an argument is not required. If used, all subsequent arguments in arglist must also be optional and declared using the Optional keyword. All Optional arguments must be Variant. Optional can't be used for any argument if ParamArray is used.
ByVal	Indicates that the argument is passed by value.
ByRef	Indicates that the argument is passed by reference.
ParamArray	Used only as the last argument in arglist to indicate that the final argument is an Optional array of Variant elements. The ParamArray keyword allows you to provide an arbitrary number of arguments. May not be used with ByVal, ByRef, or Optional.
varname	Name of the variable representing the argument being passed to the procedure; follows standard variable naming conventions.
type	Data type of the argument passed to the procedure; may be Boolean, Integer, Long, Currency, Single, Double, Date, String (variable length only), Object, Variant, a user-defined type, or an object type.

Remarks

For Function procedures, the data type of the procedure determines the data type it returns. You can use an As clause following the arglist to specify the return type of the function. Within arglist you can use an As clause to specify the data type of any of the arguments passed to the procedure. In addition to specifying any of the standard data types, you can specify As Any in the arglist to inhibit type checking and allow any data type to be passed to the procedure.

Empty parentheses indicate that the Sub or Function procedure has no arguments and that arguments should be checked to ensure that none are passed. In the following example, First takes no arguments. If you use arguments in a call to First, an error occurs:

Declare Sub First Lib "MyLib" ()

If you include an argument list, the number and type of arguments are checked each time the procedure is called. In the following example, First takes one Long argument:

Declare Sub First Lib "MyLib" (X As Long)

Note

You can't have fixed-length strings in the argument list of a Declare statement because only variable-length strings can be passed to procedures. Fixed-length strings can appear as procedure arguments, but they are converted to variable-length strings before being passed.

See Also

Call Statement.

Example

This example shows how the Declare statement is used at the module level to declare a reference to an external procedure in a dynamic-link library (DLL) or Macintosh code resource.

' In Microsoft Windows.
Declare Sub MessageBeep Lib "User" (ByVal N As Integer)

' On the Macintosh.
Declare Sub MessageAlert Lib "MyHd:MyAlert" Alias "MyAlert" (ByVal N _
As Integer)