Question

我需要创建一个C ++ dll，它具有一个函数，该函数返回要在Excel（2010）VBA代码中使用的字符串。

我已阅读以下帖子：Using C++ DLL in Excel VBA-以及Microsoft的有关C ++ dll创建和VBA使用的教程（Walkthrough: Create and use your own Dynamic Link Library (C++)，Access DLLs in Excel），并遵循了该过程。

代码如下：

C ++ dll（摘自Microsoft网页）：

// MathLibrary.h - Contains declarations of math functions
#pragma once

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

// The Fibonacci recurrence relation describes a sequence F
// where F(n) is { n = 0, a
//               { n = 1, b
//               { n > 1, F(n-2) + F(n-1)
// for some initial integral values a and b.
// If the sequence is initialized F(0) = 1, F(1) = 1,
// then this relation produces the well-known Fibonacci
// sequence: 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

// Initialize a Fibonacci relation sequence
// such that F(0) = a, F(1) = b.
// This function must be called before any other function.
extern "C" MATHLIBRARY_API void fibonacci_init(
    const unsigned int a, const unsigned int b);

// Produce the next value in the sequence.
// Returns true on success and updates current value and index;
// false on overflow, leaves current value and index unchanged.
extern "C" MATHLIBRARY_API bool fibonacci_next();

// Get the current value in the sequence.
extern "C" MATHLIBRARY_API unsigned int fibonacci_current();

// Get the position of the current value in the sequence.
extern "C" MATHLIBRARY_API unsigned fibonacci_index();

VBA代码（我的，遵循Microsoft文档）：

Public Declare Sub fibonacci_init Lib "C:\development\MathLibrary\Release\MathLibrary.dll" (ByVal a As Integer, ByVal a As Integer)
Public Declare Function fibonacci_next Lib "C:\development\MathLibrary\Release\MathLibrary.dll" () As Boolean
Public Declare Function fibonacci_current Lib "C:\development\MathLibrary\Release\MathLibrary.dll" () As Integer

Public Function run_dll()
    Dim b As Integer

    Call fibonacci_init(1, 1)
    b = fibonacci_current()
End Function

当我在VBA中运行run_dll函数时，我得到一个例外：Call fibonacci_init(1,1)行上的“错误的DLL调用约定”。

这是怎么了？我已经将C ++函数声明为extern "C"，所以我假设调用约定是固定的...

更新

我尝试过的更多事情...

我已经按照注释/答案的提示从头开始创建了一个新的dll：

Trial.cpp：

const char* str = "abcdefg";

extern "C" __declspec(dllexport) int size()
{
    return strlen(str);
}

extern "C" __declspec(dllexport) bool test(char* pReturn)
{
    int nSize = strlen(str);
    lstrcpynA(pReturn, str, nSize);

    return true;
}

具有以下VBA：

Public Declare Function size Lib "C:\development\MathLibrary\Release\Trial.dll" () As Long
Public Declare Function test Lib "C:\development\MathLibrary\Release\Trial.dll" (ByVal p As Long) As Boolean

(1) Public Function run_dll()
(2)    Dim bb As Boolean
(3)    Dim sz As Integer
(4)    Dim s As String        
(5)    sz = size()       
(6)    s = Space(sz)        
(7)    bb = test(StrPtr(s))
(8) End Function

第5行工作正常-sz收到7。但是第7行给出了“错误的DLL调用约定”。

尝试使用WINAPI声明C ++函数（如我所阅读的帖子中提到的那样）给出：Can't find DLL entry point size in C:\development\MathLibrary\Release\Trial.dll。
将test VBA声明更改为

Public Declare Function test Lib "C:\development\MathLibrary\Release\Trial.dll" (ByRef p As String) As Boolean

并以bb = test(s)调用（line7）-导致Excel崩溃

将test VBA声明更改为

Public Declare Function test Lib "C:\development\MathLibrary\Release\Trial.dll" (ByRef p As Long) As Boolean

并以bb = test(StrPtr(s))调用（line7）-给出：“错误的DLL调用约定”

似乎没有任何作用。有人为这种设置提供有效的示例吗？

Answer 1

相当于C ++整数的VBA长。

VBA中的Integer是2字节的数据类型，VBA中的Long是4字节的数据类型。由于传递的字节数与预期的字节数不匹配，因此您会得到错误的DLL调用约定

请注意，VBA不支持无符号类型，因此您的输出将被解释为带符号的4字节整数（长整数）。

Answer 2

您将需要使其成为COM库。在Windows注册表中注册它们之后，即可将它们导入VBA代码中。

从Excel VBA使用C ++ dll时出现“错误的DLL调用约定”-如何解决？

2 个答案: