Calling GetProcAddress from VBA always returns null - vba

Question

I have 64 bit windows 10 with MS Office 64 bit.
I am trying to get the VBA for Powerpoint to load and execute a function in a self-written 64 bit windows DLL.
To prevent export name mangling I have used extern C:
extern "C" {
__declspec(dllexport) long jaadd(long a, long b)
{
return a + b;
}
}
This simple function can be called by a C++ module with no problems:
hinstDLL = LoadLibrary(L"D:\\Visual Studio 2017\\Projects\\PopUpDLL\\x64\\Debug\\PopUpDLL.dll");
if (hinstDLL != NULL)
{
jaadd = (AddFunc)GetProcAddress(hinstDLL, "jaadd");
if (jaadd != NULL) {
result = jaadd(13, 40);
}
fFreeDLL = FreeLibrary(hinstDLL);
}
The problem arises when trying to call the DLL from VBA in Powerpoint. GetProcAddress always returns zero and so does FreeLibrary
Private Declare PtrSafe Function FreeLibrary Lib "kernel32" (ByVal hLibModule As Long) As LongLong
Private Declare PtrSafe Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA" (ByVal lpLibFileName As String) As Long
Private Declare PtrSafe Function GetProcAddress Lib "kernel32" (ByVal hModule As Long, ByVal lpProcName As String) As Long
Private hLib As Long
Sub LLib()
hLib = LoadLibrary("D:\\Visual Studio 2017\\Projects\\PopUpDLL\\x64\\Debug\\PopUpDLL.dll")
MsgBox hLib
Dim pprocaddress As Long
pprocaddress = GetProcAddress(hLib, "jaadd") ***** always returns 0
MsgBox pprocaddress
xx = FreeLibrary(hLib) ***** always returns 0
MsgBox xx
End Sub
Any help gratefully received.

Answer 1

Did you every try
Private Declare PtrSafe Function jaadd Lib "......\x64\Debug\PopUpDLL.dll"
Alias "_jaadd#8" (ByVal arg1 As Long, ByVal arg2 as Long) As Long
Note the Alias mangling "algorithm": _ + your original name + # + sum of argument bytes.
You have two VBA Longs, or two C# ints, 4 + 4 = 8.
You can also dispense with the twin \ thing here in VBA-land.
See also https://learn.microsoft.com/en-us/office/client-developer/excel/how-to-access-dlls-in-excel
Lastly, make sure you use a 32-bit DLL for 32-bit VBA, and a 64-bit DLL for 64-bit VBA.
So many websites in their DECLARE statements have the handle for LoadLibrary and return of GetProcAddress as Long instead of LongPtr.
Problem is that the information is stale - the code was never updated to reflect the post-Excel 2009 state of VBA.