Standard DLL

[techyspecy]

Can someone tell me how do you make Standard DLL in VC ++. I mean what project type do you select while creating a new one to create a standard dll. What properties do you set for it. Also can we write normal c++ code inside a standard DLL. I
mean no MFC or SDK etc..

[CornedBee]

Yes to the second question. You can write normal C++ code, if not you couldn't write anything. The WinAPI is just an interface after all.

As for the project, it's "Win32 DLL" in VC++6 and "Win32 Project" in VC++7. In 7 you then have to change the setting to DLL in the wizard.

[techyspecy]

Originally posted by CornedBee
Yes to the second question. You can write normal C++ code, if not you couldn't write anything. The WinAPI is just an interface after all.

As for the project, it's "Win32 DLL" in VC++6 and "Win32 Project" in VC++7. In 7 you then have to change the setting to DLL in the wizard.

Can you give me some simple code to write a standard DLL.

[sunburnt]

TestDll.cpp

#define WIN32_LEAN_AND_MEAN //exclude sockets, etc from windows header	
#include <windows.h> 
#include <math.h> // for the square root function (sqrt)

bool APIENTRY DllMain( HANDLE hModule, DWORD  ul_reason_for_call, LPVOID lpReserved )
{
    return true; // good enough for now
}

// note that this is marked extern and _stdcall
extern bool _stdcall Quadratic(double a, double b, double c, double *result1, double *result2)
{
	double tmp = (b * b) - (4 * a * c);
	if (tmp < 0) return false;

	*result1 = (-1 * b + sqrt(tmp)) / (2 * a);
	*result2 = (-1 * b - sqrt(tmp)) / (2 * a);

	return true;
}

TestDll.def

LIBRARY	TestDll

EXPORTS
	Quadratic @1
	MyOtherFunction @2
	AnotherFunction @3

to call this function from Visual Basic, you would do something like this...

Public Declare Function Quadratic Lib "TestDll.dll" (ByVal a As _
 Double, ByVal b As Double, ByVal c As Double, ByRef result1 As _
 Double, ByRef result2 As Double) As Boolean
 
Dim result1 As Double, result2 As Double
If Quadratic(1,  3, -12, result1, result2) Then
     Call MessageBox(result1 & " " & result2)
End If

[CornedBee]

VB Boolean and C++ bool are not the same.
VB Boolean uses 0xffffffff as true, C++ bool uses 0x00000001

Most likely it won't matter, but it might.

[sunburnt]

CornedBee is right, I have had that problem before. It would be better to use a return type of int and check for 0 or !0.
You would think it wouldn't matter, but inexplicably VB seems to think that this function always returns true.