I have a Delphi DLL that works when called by delphi apps and exports a method declared as:
Procedure ProduceOutput(request,inputs:widestring; var ResultString:widestring);stdcall;
On the C++ side I have tried:
[DllImport( "ArgumentLab.dll", CallingConvention = CallingConvention.StdCall, CharSet=CharSet.WideString )];
extern void ProduceOutput(WideString request, WideString inputs, WideString ResultString);
WideString arequest = WideString(ComboBox1->Text);
WideString ainput = "<xml> Input Text Goes Here </XML>";
WideString aresultstring;
WideString &aresultstringpointer = aresultstring;
aresultstring = " ";
ProduceOutput(arequest, ainput, &aresultstringpointer);
Memo1->Lines->Text = aresultstring;
My console error reads:
Unit1.cpp(13): candidate function not viable: no known conversion from 'BSTR *' (aka 'wchar_t **') to 'System::WideString' for 3rd argument;
I have built the DLL and the c++ test app using Rad Studio XE4 - it is a 64 bit DLL and APP
How should I have gone about doing this?
Best regards,
garry
There is no DllImport in C++. That is for .NET PInvoke instead. So remove that.
The remainder of your C++ function declaration does not match the Delphi function declaration. The correct C++ declaration is as follows:
void __stdcall ProduceOutput(WideString request, WideString inputs, WideString &ResultString);
Don't forget to statically link to the DLL's import .LIB file (which you can create using C++Builder's command-line IMPLIB.EXE tool, if needed).
Then, in the app's code, you can call the DLL function like this:
WideString arequest = ComboBox1->Text;
WideString ainput = "<xml> Input Text Goes Here </XML>";
WideString aresultstring;
ProduceOutput(arequest, ainput, aresultstring);
Memo1->Lines->Text = aresultstring;
The reason you are getting the conversion error is because the WideString class overrides the & operator to return a pointer to its internal BSTR member. The reason for this is to allow WideString to act like a smart wrapper class for ActiveX/COM strings, eg:
HRESULT __stdcall SomeFuncThatReturnsABStr(BSTR** Output);
WideString output;
SomeFuncThatReturnsABStr(&output);
As such, it is not possible to obtain a pointer to a WideString itself using the & operator. Because of that, the only way (that I know of) to get a real WideString pointer is to dynamically allocate the WideString, eg:
WideString *pStr = new WideString;
...
delete pStr;
Related
I have, on more than one occasion, advised people to use a return value of type WideString for interop purposes.
Accessing Delphi DLL throwing ocasional exception
ASP.NET web app calling Delphi DLL on IIS webserver, locks up when returning PChar string
Why can Delphi DLLs use WideString without using ShareMem?
The idea is that a WideString is the same as a BSTR. Because a BSTR is allocated on the shared COM heap then it is no problem to allocate in one module and deallocate in a different module. This is because all parties have agreed to use the same heap, the COM heap.
However, it seems that WideString cannot be used as a function return value for interop.
Consider the following Delphi DLL.
library WideStringTest;
uses
ActiveX;
function TestWideString: WideString; stdcall;
begin
Result := 'TestWideString';
end;
function TestBSTR: TBstr; stdcall;
begin
Result := SysAllocString('TestBSTR');
end;
procedure TestWideStringOutParam(out str: WideString); stdcall;
begin
str := 'TestWideStringOutParam';
end;
exports
TestWideString, TestBSTR, TestWideStringOutParam;
begin
end.
and the following C++ code:
typedef BSTR (__stdcall *Func)();
typedef void (__stdcall *OutParam)(BSTR &pstr);
HMODULE lib = LoadLibrary(DLLNAME);
Func TestWideString = (Func) GetProcAddress(lib, "TestWideString");
Func TestBSTR = (Func) GetProcAddress(lib, "TestBSTR");
OutParam TestWideStringOutParam = (OutParam) GetProcAddress(lib,
"TestWideStringOutParam");
BSTR str = TestBSTR();
wprintf(L"%s\n", str);
SysFreeString(str);
str = NULL;
TestWideStringOutParam(str);
wprintf(L"%s\n", str);
SysFreeString(str);
str = NULL;
str = TestWideString();//fails here
wprintf(L"%s\n", str);
SysFreeString(str);
The call to TestWideString fails with this error:
Unhandled exception at 0x772015de in BSTRtest.exe: 0xC0000005: Access violation reading location 0x00000000.
Similarly, if we try to call this from C# with p/invoke, we have a failure:
[DllImport(#"path\to\my\dll")]
[return: MarshalAs(UnmanagedType.BStr)]
static extern string TestWideString();
The error is:
An unhandled exception of type 'System.Runtime.InteropServices.SEHException' occurred in ConsoleApplication10.exe
Additional information: External component has thrown an exception.
Calling TestWideString via p/invoke works as expected.
So, use pass-by-reference with WideString parameters and mapping them onto BSTR appears to work perfectly well. But not for function return values. I have tested this on Delphi 5, 2010 and XE2 and observe the same behaviour on all versions.
Execution enters the Delphi and fails almost immediately. The assignment to Result turns into a call to System._WStrAsg, the first line of which reads:
CMP [EAX],EDX
Now, EAX is $00000000 and naturally there is an access violation.
Can anyone explain this? Am I doing something wrong? Am I unreasonable in expecting WideString function values to be viable BSTRs? Or is it just a Delphi defect?
In regular Delphi functions, the function return is actually a parameter passed by reference, even though syntactically it looks and feels like an 'out' parameter. You can test this out like so (this may be version dependent):
function DoNothing: IInterface;
begin
if Assigned(Result) then
ShowMessage('result assigned before invocation')
else
ShowMessage('result NOT assigned before invocation');
end;
procedure TestParameterPassingMechanismOfFunctions;
var
X: IInterface;
begin
X := TInterfaceObject.Create;
X := DoNothing;
end;
To demonstrate call TestParameterPassingMechanismOfFunctions()
Your code is failing because of a mismatch between Delphi and C++'s understanding of the calling convention in relation to the passing mechanism for function results. In C++ a function return acts like the syntax suggests: an out parameter. But for Delphi it is a var parameter.
To fix, try this:
function TestWideString: WideString; stdcall;
begin
Pointer(Result) := nil;
Result := 'TestWideString';
end;
In C#/C++ you will need to define the Result as out Parameter, in order to maintain binary code compatibility of stdcall calling conventions:
Returning Strings and Interface References From DLL Functions
In the stdcall calling convention, the function’s result is passed via the CPU’s EAX register. However, Visual C++ and Delphi generate different binary code for these routines.
Delphi code stays the same:
function TestWideString: WideString; stdcall;
begin
Result := 'TestWideString';
end;
C# code:
// declaration
[DllImport(#"Test.dll")]
static extern void TestWideString([MarshalAs(UnmanagedType.BStr)] out string Result);
...
string s;
TestWideString(out s);
MessageBox.Show(s);
I am using InstallShield 2013 Premium. I created a C++ dll in Visual Studio 2010 to provide some functionality I could not achieve with InstallScript alone. My C++ function needs to return a small string (a username) to the InstallScript after doing considerable work to get this value.
Throughout the C++ am I using CStringW to represent my strings. Ideally, I would like to return it as Unicode, but I'm content with ANSI if that's my only option. I have tried numerous approaches with CStringW, std::wstring, std::string, LPCTSTR, LPSTR, char *... I tried direct returns, and attempts to return by reference. Nothing works!
Sometimes the dll function hangs, sometimes it throws an exception, at best it returns garbage values with non-printing characters. The official documentation on this does not seem accurate (it doesn't work for me!). Extensive Googling, and searching the Flexera boards produce "solutions" from others struggling with the same ridiculous problem, and yet non of those work for me either...
I didn't try this until the end, as I took for granted that you could pass strings between dlls and InstallScript easily enough. In retrospect, I should have started with the interface between the two and then developed the dll functionality after that.
Thanks for the help guys! I finally figured this out for myself though. There are multiple facets to the solution, however, which I have not found documented or suggested elsewhere.
Major points
1) return a WCHAR * from C++
2) use WSTRING as the corresponding return type in the InstallScript prototype
3) return it into a regular STRING variable in InstallScript, and treat it like any other
4) retain the value the WCHAR * points to in the C++ dll in a static variable, otherwise it apparently gets deleted and the pointer becomes invalid
If you've gotten far enough to find yourself in the same boat, I probably don't need to serve up every detail, but here's a chunk of example code to help you along:
Visual Studio Def File
LIBRARY MyIsDllHelper
EXPORTS
getSomeStringW #1
C++ Header
#ifdef MYISDLLHELPER_EXPORTS
#define MYISDLLHELPER_API __declspec(dllexport)
#else
#define MYISDLLHELPER_API __declspec(dllimport)
#endif
#include <stdexcept>
#include <atlstr.h>
namespace MyIsDllHelper
{
class MyIsDllHelper
{
public:
static MYISDLLHELPER_API WCHAR * getSomeStringW();
};
}
C++ Source
#include "stdafx.h"
#include "MyIsDllHelper.h"
static CStringW someStringRetained;
CStringW getTheString()
{
CStringW s;
// do whatever...
return s;
}
WCHAR * MyIsDllHelper::MyIsDllHelper::getSomeStringW()
{
someStringRetained = getTheString();
return someStringRetained.GetBuffer( someStringRetained.GetLength() ) + L'\0';
}
InstallScript
#define HELPER_DLL_FILE_NAME "MyIsDllHelper.dll"
prototype WSTRING MyIsDllHelper.getSomeStringW();
function DoSomething( hMSI )
STRING svSomeString;
STRING svDllPath;
begin
// Find the .dll file path. (A custom function)
GetSupportFilePath( HELPER_DLL_FILE_NAME, TRUE, svDllPath );
// Load the .dll file into memory.
if( UseDLL( svDllPath ) != 0 ) then
MessageBox ("Could not load dll: " + svDllPath, SEVERE );
abort;
endif;
// Get the string from the dll
try
svSomeString = MyIsDllHelper.getSomeStringW();
catch
MessageBox( "Could not execute dll function: MyIsDllHelper.getSomeStringW", SEVERE );
abort;
endcatch;
// Remove the .dll file from memory.
if( UnUseDLL( svDllPath ) < 0 ) then
MessageBox ("Could not unload dll: " + svDllPath, SEVERE );
abort;
endif;
// Use the string
MessageBox( "svSomeString: [" + svSomeString + "]", INFORMATION );
end;
You're best off when you can make your interface use C approaches rather than C++ ones. Match the interface of functions like GetEnvironmentVariable in which your function accepts a pointer to a buffer (and for correctness a size of that buffer), and then writes into that buffer. The majority of your implementation shouldn't have to change, as long as you can finish with something like a StringCchCopy from your CString into the buffer.
Since you specifically mention CStringW and other Unicode string types, I'd suggest choosing LPWSTR (rather than LPTSTR) for the interface type.
Then all that's left is declaring this for consumption by InstallScript. This means the prototype should use WSTRING and BYREF. If the function interface is the same as GetEnvironmentVariableW, the prototype should look something like this:
prototype MyFunc(WSTRING, BYREF WSTRING, NUMBER);
You can use strings, but I guess the problem is with the encoding.
Have a look here: https://adventuresinscm.wordpress.com/2014/01/12/unicode-files-and-installshield/
I have a test dll function that reads a string and display it:
int _stdcall test(LPSTR myString) {
MessageBoxA(NULL, (LPCSTR)myString, "test", MB_OK);
return 0;}
The excel VBA declaration is
Declare Function test Lib "test.dll" (ByVal text As String) As Long
There is a sub that calls the function. It reads an excel cell with value as "abcde" and is able to display a correct result. The sub code is:
sub testCode()
test (cells(1,1).value)
end sub
However when call the dll function using excel formula =test(A1), the message box only display the first char "a" of the string.
I had spent entire weekend reading BSTR, etc, still not be able to solve this. What is going on here?
Declare your imported function as private:
Private Declare Function test_internal Lib "test.dll" Alias "test" (ByVal text As String) As Long
and create a wrapper function for Excel to use:
Public Function Test (ByVal text As String) As Long
Test = test_internal(text)
End Functin
Because apparently, while VB(A) converts string arguments to ASCII using the current system codepage when calling to Declared APIs, the Excel engine does not.
On a side note, you also might want to remove parentheses.
Excel pass a BSTR to your C++ code. Each character is coded with 2 bytes, the second one being 0 for common characters. That explains why you see only the first one, as MessageBoxA expects char* null terminated strings. Use
MessageBoxW
Try with that code
int _stdcall test( const wchar_t * pString ) {
MessageBoxW( NULL, pString, L"test", MB_OK ); // note the L prefix for literral
return 0;
}
Alternatively, you could translate the BSTR pointer to a char* one, using some ATL macros, or raw Win32 APIs as WideCharToMultiByte (more tricky, mush simpler to use ATL)
I'm not able to use the function of a dll developed in delphi. I'm having some difficulties with the conversions of types.
This is the function I want to call the DLL:
function rData(ID: Cardinal; queue: WideString): WideString; stdcall;
My code in C++ was so:
typedef string (*ReturnDataSPL)(DWORD, string);
string result;
HMODULE hLib;
hLib = LoadLibrary("delphi.dll");
pReturnDataSPL = (ReturnDataSPL)GetProcAddress(hLib,"rData");
if (NULL != pReturnDataSPL)
result = pReturnDataSPL(JobID,printerName);
The problem I'm not able to make it work. I do not know which type is compatible with Delphi WideString and Cardinal.
Someone help me
EDIT:
This is the function I want to call the DLL:
procedure rData(ID: Cardinal; queue: WideString; var Result: WideString); stdcall;
After changing the code looked like this:
typedef void (__stdcall *ReturnDataSPL)(DWORD, BSTR, BSTR&);
HMODULE hLib;
BSTR result = NULL;
hLib = LoadLibrary("delphi.dll");
pReturnDataSPL = (ReturnDataSPL)GetProcAddress(hLib,"rData");
if (NULL != pReturnDataSPL)
{
pReturnDataSPL(JobID,(BSTR)"Lexmark X656de (MS) (Copiar 2)",result);
}
You've got very little chance of calling that function.
For a start your current code can't hope to succeed since I presume string is std::string. That's a C++ data type which Delphi code cannot either provide or consume. To match up against Delphi's WideString you need to use the COM BSTR data type.
Another problem with your code as it stands is that it uses cdecl in the C++ side, and stdcall on the Delphi side. You'll need to align the calling conventions.
However, that will also fail because of a difference between Delphi's ABI for return values, and the platform standard. That topic was covered in detail here: Why can a WideString not be used as a function return value for interop?
Your best bet is to stop using WideString as a return value and convert it into a C++ reference parameter. You'll want to convert the Delphi to match.
You are looking at something like this:
Delphi
procedure rData(ID: Cardinal; queue: WideString; var Result: WideString); stdcall;
C++
typedef void (__stdcall *ReturnDataSPL)(DWORD, BSTR, BSTR&);
I have a code in C++ that calls functions from external library. The function I called is CreateProcess like below.
CreateProcess(NULL,pProcessName,NULL,NULL,false,CREATE_SUSPENDED,
NULL,NULL,&suStartUpInformation,&piProcessInformation)
Now when I compile the code and dissemble it, the assembly shows the plain text as CreateProcess(args1, args2, ...). Is there any way to obfuscate or encrypt the function call to API so that if someone dissembles it then he won't ever know which functions are called.
Thanks!
Any function that is imported by name will always have the name embedded into the binary (in the import descriptor thunk to be exact), the detailed parameter info is gotten from the pdbs as Steve mentioned (however analysing debuggers like ollydbg can deduce args, due to the symbol name being available). The only ways to avoid this is to either encrypt to IAT (using 3rd party packers/virtualizers/binary protection systems etc, like enigma) or use a custom version of GetModuleHandle (basically just a PEB spelunking tool) and GetProcAddress (a PE spelunking tool this time), then by storing all the api calls you need as runtime encrypted strings, you can then call whatever you need without plain text giving you away (securerom does this, though it uses GetProcAddress directly, along with some binary obfuscation).
Update:
for compile-time 'obfuscated' strings, you can use something like this (really simple, but it should be portable, if you use C++0x, this is a lot easier):
#define c(x) char((x) - 1) //really simple, complexity is up to the coder
#define un(x) char((x) + 1)
typedef int (WINAPI* MSGBOX)(HWND, LPCSTR, LPCSTR, UINT);
const int ORD_MASK = 0x10101010;
const char szMessageBoxA[] = {c('M'),c('e'),c('s'),c('s'),c('a'),c('g'),c('e'),c('B'),c('o'),c('x'),c('A')};
FARPROC GetProcAddressEncrypted(HMODULE hModule, const char* szName, BOOL bOrd = FALSE)
{
if(bOrd)
return GetProcAddress(hModule,reinterpret_cast<const char*>(reinterpret_cast<int>(szName) ^ ORD_MASK)); //this requires that ordinals be stored as ordinal ^ ORD_MASK
char szFunc[128] = {'\0'};
for(int i = 0; *szName; i++)
szFunc[i] = uc(*szName++);
return GetProcAddress(hModule,szName);
}
MSGBOX pfMsgBox = static_cast<MSGBOX>(GetProcAddressEncrypted(GetHandleEncrypted(szUser32),szMessageBox));
Optionally you may want to use MSVC's EncodePointer to hide the values in the global function pointers (just remember to use DecodePointer when you call them).
note: code is untested, as its just off the top of my head
You might use dynamic linking. In Windows, use LoadLibrary, LoadLibraryEx, GetProcAddress. Now in you code, include some form in obfuscated form of name instead of the real lib/symbol names and unofuscate it at runtime.
You might want to use dynamic dispatch (function pointers) so that the function called cannot be deduced easily from the code.
You might delegate the work of calling this function to another thread (using some IPC mechanism).
But it's quite useless, using a debugger it will very simple to find that this function has been called. And it will be very simple to detect that a process has been created.
Ok! here is the solution. Lets say I want to call "MessageBoxA" from "user32.dll".
So here is how I will do it using LoadLibraryA & GetProcAddress .
//Ok here you can see.
//I am passing DLL name(user32.dll) and DLL function(MessageBoxA) as String
//So I can also perform Encrypt & Decrypt operation on Strings and obfuscate it.
//Like i can encrypt the string "user32.dll" and at runtime decrypt it and pass it as
//an argument to "LoadLibraryA" and same for the Function name "MessageBoxA".
//The code is compiled in DevC++ 4.9.9.2.
#include <windows.h>
#include <iostream>
using namespace std;
void HelloWorld()
{
char* szMessage = "Hello World!";
char* szCaption = "Hello!";
HMODULE hModule = LoadLibraryA( "user32.dll" );
FARPROC fFuncProc = GetProcAddress( hModule, "MessageBoxA" );
( ( int ( WINAPI *)( HWND, LPCSTR, LPCSTR, UINT ) ) fFuncProc )( 0, szMessage, szCaption, 0 );
}
int main()
{
HelloWorld();
}