如何通过DLL函数的参数将变量返回到Excel

How to return a variable through an argument of a DLL function to Excel?

本文关键字：变量 返回 Excel 参数 何通过 DLL 函数      更新时间：2023-10-16

我有一个C++函数，通过使用VC2013:构建的DLL在Excel 2013中使用

double my_function(double input) {
//do something
return input*input;
}

在Excel VBA中，我包含这样的函数：

Declare Function my_function Lib "DLL_with_my_function.dll" (ByVal input As Double) As Double

到目前为止，这一切都很好，但是，现在，我希望能够通过第二个参数返回第二条信息，比如错误代码。理想情况下，这个错误代码可以输出到Excel中的一个单元格，或者至少可以通过debug.print输出到控制台。这是我徒劳的尝试：

double my_function(double input, long *error_code) {
*error_code = 5;
return input*input;
}
#in Excel:    
Declare Function my_function Lib "DLL_with_my_function.dll" (ByVal input As Double, ByRef error_code as long) As Double

当我从工作表中调用函数并将单元格指示为第二个参数时，Excel会崩溃。正确、优雅的方法是什么？

您不能将exel单元格作为长数字赋予c\c++，因为它不会自动转换

你可以这样做：

double my_function(double input, long *error_code) {
  *error_code = 5;
  return input*input;
}
//unless you don't want to build the long from bytes, you can use function to do so. 
long get_error_code(long* error_code ){
  return *error_code;
}

在Excel中也声明新函数：

Declare Function my_function Lib "DLL_with_my_function.dll" (ByVal input As Double, ByVal error_code as long) As Double
Declare Function get_error_code Lib "DLL_with_my_function.dll" (ByVal error_code as long) As Long
#now in the function you should allocate memory to the error code:
Dim hMem As Long, pMem As Long
#hMem is handle to memory not a pointer
hMem = GlobalAlloc(GMEM_MOVEABLE Or GMEM_ZEROINIT, 10) 
#pMem is your pointer     
pMem = GlobalLock(hMem)
#now you can call to my_function with the pointer:
retval = my_function(input, pMem)
#in VB there is auto cast so this will work: 
YourCell = get_error_code(pMem)
# Unlock memory make the pointer useless
x = GlobalUnlock(hMem)
# Free the memory
x = GlobalFree(hMem)
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