Description

 

Sometimes it is not possible to directly declare an external function or sub because there is no way to know in which library it is.

To solve this problem, thinBasic allows declaration of external functions or sub without having the library name and alias. thinBasic will store all function or sub information for subsequent usage.

 

Later, where there will be the possibility to know the function address, you can assign that address to the declared function in order to be able to call it. To assign the address, see DECLARE SET ADDRESS statement.

 

Syntax

 

DECLARE {SUB | FUNCTION} ProcName [([Arguments])] [AS ReturnType] [AT Address]

 

Returns

 

None

 

Parameters

 

 

Remarks

 

To be able to use the general declared function or sub, it has to be assigned a process address using DECLARE SET ADDRESS statement.

 

This statement is needed only for external functions or inline functions created with machine code. It has nothing to share with standard functions or subs defined inside the script source code.

Many programming languages use DECLARE statement to let the parser know about functions present inside the source code and maybe used in the code before their declaration. This is mainly done because those languages make just one single parsing pass. This is not necessary in thinBasic because thinBasic makes all the necessary steps to automatically detect functions present in source code. Do not use DECLARE statement to describe source functions.

 

Restrictions

 

See also

 

DECLARE SET ADDRESS

 

Examples

 

'---

'---Standard API functions to get a function address. Those functions are used to simulate Petr SomeDirtyAPIToTellMeHandle function

'---

Declare Function LoadLibrary    Lib "KERNEL32.DLL" Alias "LoadLibraryA"   (lpLibFileName As ASCIIZ) As Long

Declare Function GetProcAddress Lib "KERNEL32.DLL" Alias "GetProcAddress" (ByVal hModule As DWORD, lpProcName As ASCIIZ) As Long

 

 

'---Commented line is a standard API declare for IsCharUpper function. We will not use this way in this example but ... (see next comment)

'DECLARE FUNCTION IsCharUpper LIB 'USER32.DLL' ALIAS 'IsCharUpperA' (BYVAL cChar AS BYTE) AS LONG

 

'--- ...we will tell thinBasic you are defining a generic function not jet initialized (ie, library and address are missing)

Declare Function IsCharUpper (ByVal cChar As Byte) As Long

 

 

'---OK, here we start simulating the assigment of the procedure address

Dim hLib As Long

Dim hProc As Long

 

'---First we need to load the library from where we want the address of the function

hLib = LoadLibrary("USER32.DLL")

'---If return value is NOT zero all is ok

If hLib <> 0 Then

  '---Now we try to get the address of the prodecure inside the library

  hProc = GetProcAddress(hLib, "IsCharUpperA")

  '---If return value is NOT zero all is ok

  If hProc <> 0 Then

 

    '---

    '---Here the new thinBasic functionality. It assign a process address to a generic previously declared function allowing subsequent calling

    Declare Set ADDRESS IsCharUpper, hProc

    '---So we are telling thinBasic that the previous declared function 'IsCharUpper' has now its process address

 

    '---Now we try to use the new functionality that will tell us if a char is upper or not

    Dim Char As String VALUE "F"

    Dim AsciiChar As Byte VALUE ASC(Char)

    MSGBOX 0, "OK. IsCharUpper for char " & Char & " returned: " & IsCharUpper(AsciiChar) & " (1=true and 0= false)"

  Else

    MSGBOX 0, "It was not possible to get the procedure address"

  End If

Else

  MSGBOX 0, "It was not possible to load library"

End If