Using the Declare Statement
API routines are outside of VB's entire scope, so
you must use Declare statement to give VB information
about the API function you're calling. The Declare
statement performs the following tasks:
- Specifies where the API function is located.
- Identifies arguments needed by the API function
by number and data type.
- Specifies whether or not the API function returns
a value.
Procedures
Declare Sub name Lib "libname" [Alias "aliasname"][([arglist])]
Functions
Declare Function name Lib "libname" [Alias
"aliasname"][([arglist])] [As type]
API Data Types
One of the reasons the API routines are difficult
to call is that Windows uses a slightly different
set of data types than VB. The following table lists
some of the data types:
| Data Type |
Description |
| ANY |
It accepts different
kinds of data types. All ANY arguments are passed
by reference, so you won't use the ByVal keyword. |
| ATOM |
Integer Data.
Always passed by value. |
| BOOL |
An expression
that evaluates to a Long. Always passed by value. |
| CHAR |
An expression
that evaluates to a Byte. Always passed by value. |
| COLOREF |
An expression
that evaluates to a Long. Always passed by value. |
| DWORD |
An expression
that evaluates to a Long. Always passed by value. |
| NULL |
Long integer
data types used for uninitialized values. |
| LPSTR, LPCSTR |
An expression
that evaluates to a String. Described in an
API routine's declaration as ByVal argument$
or ByVal argument As String. |
|
