Microsoft Access 2010 Bible

Chapter 27: Using the Windows Application Programming Interface

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Dim strMyString As String

strMyString = String$(20,” “)

The preceding code fills the fixed-width string variable strMyString with 20 spaces. You can

achieve the same result by declaring the string with the number of characters already allocated:

Dim strMyString * 20

Caution
If you don’t allocate enough space for an API function to write a string, it could end up writing over another
application’s data, causing an error. It’s very difficult to know how many characters an API will accept, so a
safe way to declare your string variables is to allocate 255 characters to string variables. Most functions will
not pass a string larger than 255 characters.

As DataType

Any API call that is a function returns a value. A subroutine does not. The value returned by a

function is usually a value that you use in your application, or it’s an error number. For example,

many functions return zero, or ERROR_SUCCESS if the function completes successfully. In this

case, if the value returned is not zero (indicating that the API call failed to execute properly), you

should provide an error-handling routine to deal with the function’s failure.

Other functions, such as GetPrivateProfileStringA, return a numeric value indicating the

number of characters copied into a string buffer. Therefore, if GetPrivateProfileStringA

completes successfully, you use its return value and the Left$() function to extract the returned

string from a string buffer.

StringVar = Left$(StringBuffer, ReturnValue)

If the value returned by GetProfileStringA is 0 , of course, it means that no string was found

in the .ini file.

The data type specified for the return value must be compatible with the data type specified in the

API function’s documentation.

Wrapper functions

You rarely directly program API functions. API calls frequently require complicated arguments,

and the values returned by API functions most often require interpretation before they can be used.

Many developers use wrapper functions to resolve these issues. A wrapper function is a simple VBA

procedure that provides the API call with all the parameters it needs, as well as converting the val-

ues returned by the API function to a format the application can use. Your VBA code calls the

wrapper function, which, in turn, calls the API function. The wrapper function returns the trans-

formed value provided by the API function.