CALL32.DLL: 32-bit DLL calling library for Visual Basic by Peter Golde This program is placed in the public domain. Please feel free to redistribute as you wish. No guarantees are made as to its suitability or usefulness, and no support can be provided. 1. Summary ---------- CALL32.DLL is a DLL that can be used for calling routines in 32-bit DLLs on Windows NT. It cannot be used on Windows 3.1, Win32s, Chicago, or other operating systems. Using it, a Visual Basic program, running in the Win16 subsystem, can declare and call functions in any 32-bit DLL (including, but not limited to, the system DLLs). CALL32.DLL works on both the x86 and MIPS versions on NT. It has not been tested on Alpha or other versions, but should work. 2. Usage -------- To call a function in a 32-bit DLL, follow the following steps. Declare the "Declare32" function as follows (all one one line): Declare Function Declare32 Lib "call32.dll" (ByVal Func$, ByVal Library$, ByVal Args$) As Long Next, declare the function you wish to call. Declare it in the ordinary fashion, with the following exceptions: - Use a library name of "call32.dll" - Use an Alias of "Call32" - Add an additional argument at the end, of type ByVal Long For example, if you are calling the function: GetWindowText(HWND hwnd, LPSTR lpsz, int cch) declare it as follows (remember that ints and all handles are 32 bits, so use a Long): Declare Function GetWindowText Lib "call32.dll" Alias "Call32" (ByVal hwnd As Long, ByVal lpsz As String, ByVal cch As Long, ByVal id As Long) As Long In the initialization section of your application, you declare the actual library and name of the function you want to call with the Declare32 function. Pass it the name of the function, the library, and a string describing the argument types. Each letter in the string declares the type of one argument, and should be either "i" for a 32 bit integer or handle type, "p" for any pointer type, or "w" for an HWND parameter you want to pass a 16 bit HWND to and have be automatically converted to a 32 bit HWND. The return value of Declare32 should be saved away in a global variable to be passed as the last parameter to the function you declared earlier. So, continue the example, you would call: idGetWindowText = Declare32("GetWindowText", "user32", "wpi") (As a side note, this would be more properly declared as "GetWindowTextA", since this is the real exported name. However, Declare32 will automatically add an "A" to the end of a function name if necessary). To call the function, you would just call: cbCopy = GetWindowText(hwnd, sz, cb, idGetWindowText) 3. Data Types and Handles ------------------------- It is important to use the correct data types when calling DLL functions. There are two important points to pay attention to when using CALL32.DLL. First, only 32 bit integers can be passed to a DLL procedures. Since virtually all 32 bit functions take int, UINT, LONG, DWORD, or HANDLE parameters, which are all 32 bits, this is not a major restriction. However, you must remember to always declare functions arguments are Long, and not Integer. Secondly, 16 bit handles and 32 bit handles are not interchangable. For example, a 16 bit bitmap handle that you get from calling a 16 bit DLL or from the VB environment cannot be passed to a 32 bit function expecting a bitmap handle. Similarly, a 32 bit handle gotten from a 32 bit function cannot be passed to a 16 bit DLL. The only exception is window handles (HWND). If you declare a function parameter with the "w" letter in the argument description string passed to Declare32, the corresponding parameter will be automatically converted from a 16 bit HWND to a 32 bit HWND when the call is made. You must still declare the argument as a LONG. This is convenient, for example, when passing the value returned by the "hWnd" property of a control to a 32 bit DLL function. Only windows created by your application can be translated. Summary of data types: C data type Type specified in Declare Character for Declare32 int, UINT ByVal Long i LONG, DWORD ByVal Long i HANDLE ByVal Long i WORD, short not supported HWND ByVal Long w (i for no 16->32 translation) LPSTR ByVal String p LPLONG, LPDWORD, LPUINT, int FAR * Long p LPWORD Integer p 4. Note on Declare32 function names ----------------------------------- Declare32 will automatically try three different names for the function name you pass in. First, it uses the exact name you pass in. If that function name isn't found, it converts the name to the stdcall decorated name convention, by adding an underscore at the beginning, and adding "@nn" at the end, where "nn" is the number of bytes of arguments. If that name isn't found, it adds an "A" to the end of the original name to try the Win32 ANSI function calling convention. 5. Run-time Error Summary ------------------------- The following run-time errors can be generated by CALL32.DLL 30001 Can't load DLL: "|" (error=|) The DLL name passed to Declare32 was not the name of a valid 32 bit DLL. The Win32 error code is specified at the end of the error message, this can help determine why the DLL didn't load. 30002 Can't find specified function The function name passed to Declare32 could not be found in the DLL. 30003 Invalid parameter definition string The parameter definition string passed to Declare32 had an invalid character in it, or was too long (32 parameters is the limit). 30004 Not running on Windows NT The program is not running in the Windows16 subsystem of Windows NT. 30005 Invalid window handle The 16 bit window handle passed as a parameter declared with the 'w' character was not a valid 16 bit window handle, or refers to a window from a different process. 6. Change History ------------------ 1.00 Original Version (8/31/93) 1.01 Better error message when DLL can't be loaded (9/27/93) Stdcall name decoration support Source code available Sample Bezier program from Adam Rauch