Alright, let's break down how to get your compiled C++ DLL working with VBA, using the dumpbin output you shared. First, a quick note: your DLL exports mangled C++ function names (like ?Add@Functions@MathLibrary@@SANNN@Z), which means these are C++-style functions (likely part of a namespace or class). Here's what you need to do:

1. Understand Your Function Signatures & Calling Convention #

From the mangled names, we can parse key details:

• The Add function, for example, returns a double and takes two double parameters (the NN in the mangled name stands for double, and SAN points to the return type + calling convention).
• The A in the mangled name tells us the function uses the __cdecl calling convention (VBA's default is __stdcall, so we'll need to account for this mismatch).

2. Declare the DLL Functions in VBA #

You have two options here, depending on whether you can recompile your DLL or not.

Option 1: Use the Mangled Export Names (If You Can't Recompile) #

Since your DLL already has mangled names, you'll need to reference those exact names in your VBA declarations. Open the VBA editor (press Alt+F11 in Excel/Office), insert a new module, and add this code:

' Replace the path with your actual DLL file path
Declare Function MathLib_Add Lib "C:\Path\To\HelloDLL.dll" _
    Alias "?Add@Functions@MathLibrary@@SANNN@Z" _
    (ByVal a As Double, ByVal b As Double) As Double Cdecl

Declare Function MathLib_AddMultiply Lib "C:\Path\To\HelloDLL.dll" _
    Alias "?AddMultiply@Functions@MathLibrary@@SANNN@Z" _
    (ByVal a As Double, ByVal b As Double) As Double Cdecl

Key notes here:

• Lib: Specify the full path to your DLL (or just the filename if it's in a system/Office directory).
• Alias: Must match the exact mangled name from dumpbin (case and symbols matter!).
• Cdecl: Critical here—since your C++ function uses __cdecl, adding this ensures VBA uses the correct calling convention (omitting this will cause stack errors).
• Parameter types: Double in VBA maps directly to C++'s double, and ByVal ensures we pass values correctly.

Option 2: Recompile the DLL with extern "C" (Cleaner Approach) #

If you can recompile your C++ library, you can avoid mangled names entirely by using extern "C" to export functions in a C-compatible style. Modify your C++ code like this:

#include <cmath>

namespace MathLibrary {
    class Functions {
    public:
        // Export with C linkage to avoid name mangling
        extern "C" __declspec(dllexport) double __cdecl Add(double a, double b) {
            return a + b;
        }

        extern "C" __declspec(dllexport) double __cdecl AddMultiply(double a, double b) {
            return (a + b) * a;
        }
    };
}

After recompiling, your dumpbin output will show clean, unmangled names like Add and AddMultiply. Then your VBA declaration simplifies to:

Declare Function Add Lib "HelloDLL.dll" _
    (ByVal a As Double, ByVal b As Double) As Double Cdecl

Declare Function AddMultiply Lib "HelloDLL.dll" _
    (ByVal a As Double, ByVal b As Double) As Double Cdecl

3. Call the Functions in VBA #

Once you've declared the functions, you can use them in any VBA procedure. For example:

Sub TestDLLFunctions()
    Dim addResult As Double
    Dim addMultiplyResult As Double
    
    addResult = MathLib_Add(2.5, 3.5) ' Or just Add() if you used Option 2
    addMultiplyResult = MathLib_AddMultiply(2.5, 3.5) ' Or AddMultiply()
    
    MsgBox "Add Result: " & addResult & vbCrLf & "AddMultiply Result: " & addMultiplyResult
End Sub

Critical Gotchas to Avoid #

• Bitness Match: Make sure your DLL's architecture matches your Office installation (64-bit DLL for 64-bit Office, 32-bit for 32-bit). Mismatches will throw "module not found" errors.
• Calling Convention Consistency: If you switch your C++ function to __stdcall, remove the Cdecl keyword from your VBA declaration (VBA uses __stdcall by default).
• Path Accuracy: Always test with the full DLL path first—relative paths can cause issues if the DLL isn't in a system-wide search directory.

内容的提问来源于stack exchange，提问作者Fabian Schneider