Excel VBA，无法从 DLL 文件中找到 DLL 入口点

问题描述

我正在尝试使用 Excel VBA 的功能来访问和使用 DLL 文件中的函数.

示例:

私有声明函数funcName Lib _""_(ByRef a As Double, ByRef b As Double) As Double

<小时>

按照

但无论如何，这个警告是良性的，.dll 仍然被构建，并且符号被导出.

更进一步，在您的 VBA 模块中声明函数名称 Add(纯文本).基于错误消息:

在pathfile.dll"中找不到 DLL 入口点添加

正如我在我的评论中指出的那样，我认为 Excel 无法导入 C++ 样式导出，因为

您应该从 Excel 导入的那些(胡言乱语)名称，但我怀疑这是可能的.作为一种解决方法，您可以:

• 删除 C++ 特性(类和命名空间)并定义和导出 3 个简单函数
• 编写 3 个 C 函数(封装了 3 个方法)，并导出函数而不是方法

[SO]: 在不同的 VS2010 项目中从 C++ 代码调用 C 函数时出现链接器错误(@CristiFati 的回答) 包含所有细节(注意 extern "C": [MS.Docs]:extern (C++)).>

I am attempting to use Excel VBA's ability to access and use functions from DLL files.

example:

Private Declare Function funcName Lib _
"<filePathFile.dll>" _
(ByRef a As Double, ByRef b As Double) As Double

Following the instructions from Mircosoft's tutorial on how to create a DLL file, leads to 3 warnings (C4273) when I try to build the project, for the 3 functions declared:

'MathLibrary::Functions::Add': inconsistent dll linkage,
'MathLibrary::Functions::Multiply': inconsistent dll linkage,
'MathLibrary::Functions::AddMultiply': inconsistent dll linkage

When the VBA in Excel tries to access the created .dll file from this tutorial, it produces a runtime error (453): 'Can't find DLL entry point Add in "pathfile.dll".

I am a novice when it comes to the CC++ language. I have spent over 6 hours of:

• trying to make tweaks to the vanilla tutorial
• starting over
• googling for help, and similar issues
• making tweaks to the statements within VBA

And yet I feel further from a solution.

I am running 32-bit Excel on 64-bit Windows.

Any help would be much appreciated :)

Edit

Code Files (as requested):

MathLibrary.cpp

// MathLibrary.cpp : Defines the exported functions for the DLL application.
// Compile by using: cl /EHsc /DMATHLIBRARY_EXPORTS /LD MathLibrary.cpp  

#include "stdafx.h"  
#include "MathLibrary.h"  

namespace MathLibrary
{
    double Functions::Add(double a, double b)
    {
        return a + b;
    }

    double Functions::Multiply(double a, double b)
    {
        return a * b;
    }

    double Functions::AddMultiply(double a, double b)
    {
        return a + (a * b);
    }
}

MathLibrary.h

// MathLibrary.h - Contains declaration of Function class  
#pragma once  

#ifdef MATHLIBRARY_EXPORTS  
#define MATHLIBRARY_API __declspec(dllexport)   
#else  
#define MATHLIBRARY_API __declspec(dllimport)   
#endif  

namespace MathLibrary
{
    // This class is exported from the MathLibrary.dll  
    class Functions
    {
    public:
        // Returns a + b  
        static MATHLIBRARY_API double Add(double a, double b);

        // Returns a * b  
        static MATHLIBRARY_API double Multiply(double a, double b);

        // Returns a + (a * b)  
        static MATHLIBRARY_API double AddMultiply(double a, double b);
    };
}

stdafx.h

// stdafx.h : include file for standard system include files,
// or project specific include files that are used frequently, but
// are changed infrequently
//

#pragma once

#include "targetver.h"

#define WIN32_LEAN_AND_MEAN             // Exclude rarely-used stuff from Windows headers
// Windows Header Files:
#include <windows.h>

// TODO: reference additional headers your program requires here

targetver.h

#pragma once

// Including SDKDDKVer.h defines the highest available Windows platform.

// If you wish to build your application for a previous Windows platform,
//     include WinSDKVer.h and
// set the _WIN32_WINNT macro to the platform you wish to support 
//     before including SDKDDKVer.h.

#include <SDKDDKVer.h>

VBA Module

Private Declare Function Add Lib _
"c:<Path>MathLibrary.dll" _
(ByRef a As Double, ByRef b As Double) As Double

Sub useAddXL()
    MsgBox Add(1, 2)
End Sub

I'm going to post this in a solution, as it doesn't fit in an comment.

The "inconsistent dll linkage" warning: I copied your exact code from the question as it is at this point (it might change in the future), and placed it in a newly created VStudio 2015 project:

• Configuration type: Dynamic Library (.dll)
• Using precompiled headers (although, I usually don't do it)

The project compiled with no warnings, if I define MATHLIBRARY_EXPORTS either:

• In the MathLibrary.cpp file #define MATHLIBRARY_EXPORTS (before #include "MathLibrary.h")
• As a project setting: adding it under Project Properties -> Configuration Properties -> C/C++ -> Preprocessor -> Preprocessor Definitions (next to other macros, separated by semicolons (;))

The only thing that I can imagine for you to still get the warning when building yours, is because you are defining the macro for the wrong configuration.
Example: you are building your project for Debug - x86, but you define the macro for Release - x86 (or Debug - x64).
You must check (it would be better select All Platfroms and All Configurations, and only define the macro once) that build configurations and settings configurations match, like in the image below:

But anyway, this warning is benign, the .dll is still built, and the symbols exported.

Going further, in your VBA module you declare the function name Add (plain). Based on the error message:

Can't find DLL entry point Add in "pathfile.dll"

as I specified on one of my comments, I don't think that Excel is able to import C++ style exports because of [MS.Docs]: Decorated Names (C++ name mangling). While it searches for Add, your .dll exports the following symbols as shown in the (Dependency Walker) image below (you can play with the highlighted button and see how Dependency Walker is able to demangle those names):

Those (gibberish) names you should import from Excel, but I doubt that's possible. As a workaround you could either:

• Drop the C++ features (the class and the namespace) and define and export 3 simple functions
• Write 3 C functions (wrappers over the 3 methods), and export the functions not the methods

[SO]: Linker error when calling a C function from C++ code in different VS2010 project (@CristiFati's answer) contains all the details (pay attention on extern "C": [MS.Docs]: extern (C++)).

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