Pascal Scripting: Using DLLs

The Pascal script can call functions inside external DLLs. This includes both standard Win32 API functions inside standard Windows DLLs and custom functions in custom made DLLs (how to make such a custom DLL is beyond the scope of this help file).

To be able to call a DLL function you should first write the function prototype as normal but instead of then writing the function body, you use the 'external' keyword to specify a DLL. If your function has for example prototype function A(B: Integer): Integer;, the following three forms are supported:

function A(B: Integer): Integer;
external '<dllfunctionname>@<dllfilename>';

function A(B: Integer): Integer;
external '<dllfunctionname>@<dllfilename> <callingconvention>';

function A(B: Integer): Integer;
external '<dllfunctionname>@<dllfilename> <callingconvention> <options>';

The first form specifies that the DLL function should be called using default calling convention, which is 'stdcall'. All standard Win32 API functions use 'stdcall' just like most custom DLL functions.

The second form specifies that the DLL function should be called using a special calling convention. Valid calling conventions are: 'stdcall' (the default), 'cdecl', 'pascal' and 'register'.

The third form specifies additional one or more options for loading the DLL, separated by spaces:

delayload: Specifies that the DLL should be delay loaded. Normally the Pascal script checks at startup whether the DLL function can be called and if not, refuses to run. This does not happen if you specify delay loading using 'delayload'. Use delay loading if you want to call a DLL function for which you don't know whether it will actually be available at runtime: if the DLL function can't be called, the Pascal script will still run but throw an expection when you try to call the DLL function which you can catch to handle the absence of the DLL function.
setuponly: Specifies that the DLL should only be loaded when the script is running from Setup.
uninstallonly: Specifies that the DLL should only be loaded when the script is running from Uninstall.

An example (of the second form) if the DLL function has name 'A2' inside the DLL, the DLL has name 'MyDll.dll' and the DLL function uses the 'stdcall' calling convention:

[Code]
function A(B: Integer): Integer;
external 'A2@MyDll.dll stdcall';

Constants may be used in the DLL filename. During Setup, a special 'files:' prefix to instruct Setup to automatically extract the DLL from the [Files] section may also be used. For example:

[Files]
Source: "MyDll.dll"; Flags: dontcopy

[Code]
procedure MyDllFunc(hWnd: Integer; lpText, lpCaption: String; uType: Cardinal);
external 'MyDllFunc@files:MyDll.dll stdcall';

Open the "CodeDll.iss" file in the "Examples" subdirectory in your Inno Setup directory for an example script using DLLs.

The "Examples" subdirectory also contains two custom DLL example projects, one for Microsoft Visual C++ and one for Borland Delphi.