Mega Code Archive
How to call a DLL function with variable RT parameter dynamically
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Title: How to call a DLL function with variable RT-parameter dynamically
// Calls a function from a library.
// if it's not loaded yet, it will call LoadLibrary() to load it.
function DynamicDllCallName(Dll: String; const Name: String; HasResult: Boolean; var Returned: Cardinal; const Parameters: array of Pointer): Boolean;
var
prc: Pointer;
x, n: Integer;
p: Pointer;
dllh: THandle;
begin
dllh := GetModuleHandle(PChar(Dll));
if dllh = 0 then begin
dllh := LoadLibrary(PChar(Dll));
end;
if dllh 0 then begin
prc := GetProcAddress(dllh, PChar(Name));
if Assigned(prc) then begin
n := High(Parameters);
if n -1 then begin
x := n;
repeat
p := Parameters[x];
asm
PUSH p
end;
Dec(x);
until x = -1;
end;
asm
CALL prc
end;
if HasResult then begin
asm
MOV p, EAX
end;
Returned := Cardinal(p);
end else begin
Returned := 0;
end;
end else begin
Returned := 0;
end;
Result := Assigned(prc);
end else begin
Result := false;
end;
end;
// Calls a function from a loaded library
function DynamicDllCall(hDll: THandle; const Name: String; HasResult: Boolean; var Returned: Cardinal; const Parameters: array of Pointer): Boolean;
var
prc: Pointer;
x, n: Integer;
p: Pointer;
begin
prc := GetProcAddress(hDll, PChar(Name));
if Assigned(prc) then begin
n := High(Parameters);
if n -1 then begin
x := n;
repeat
p := Parameters[x];
asm
PUSH p
end;
Dec(x);
until x = -1;
end;
asm
CALL prc
end;
if HasResult then begin
asm
MOV p, EAX
end;
Returned := Cardinal(p);
end else begin
Returned := 0;
end;
end else begin
Returned := 0;
end;
Result := Assigned(prc);
end;
Usage Examples: 1.GetSystemDirectory
var
parameters: array of Pointer;
returned: Cardinal;
Dir: String;
begin
SetLength(parameters, 2);
SetLength(Dir, MAX_PATH); // Set Buffer size
parameters[0] := Pointer(@Dir[1]); // 1st parameter, buffer for path string
parameters[1] := Pointer(MAX_PATH); // 2nd parameter, length of buffer
if not DynamicDllCallName(kernel32, 'GetSystemDirectoryA', true, returned, parameters) then begin
ShowMessage('Function could not be found!');
end else begin
SetLength(Dir, returned); // Cut String
ShowMessage('GetSystemDirectoryA:'#13#10'Path: ' + Dir + #13#10'Length: ' + IntToStr(returned));
end;
end;
Usage Examples: 2.TextOut
const
SampleText = 'test';
var
parameters: array of Pointer;
returned: Cardinal;
begin
SetLength(parameters, 5);
parameters[0] := Pointer(Canvas.Handle); // 1st parameter, handle to the form's canvas
parameters[1] := Pointer(10); // 2nd parameter, left margin
parameters[2] := Pointer(30); // 3rd parameter, top margin
parameters[3] := @SampleText[1]; // 4th parameter, pointer to the sample string
parameters[4] := Pointer(Length(SampleText)); // 5th parameter, length of the sample string
if not DynamicDllCallName(gdi32, 'TextOutA', true, returned, parameters) then begin
ShowMessage('Function could not be found!');
end else begin
if not BOOL(returned) then begin // function's result = false
ShowMessage('TextOut() failed!');
end;
end;
end;
Usage Examples: 3.LockWorkStation
var
parameters: array of Pointer;
returned: Cardinal;
begin
// We don't have parameters, so we don't touch parameters
if not DynamicDllCallName(user32, 'LockWorkStation', true, returned, parameters) then begin
ShowMessage('Function could not be found!');
end else begin
if not BOOL(returned) then begin
ShowMessage('LockWorkStation() failed!');
end;
end;
end;
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