C#调用返回结构的C++ DLL函数

Question

我有一个 C++ dll，它定义了一个结构和一个 dll 调用，如下所示：

typedef const char* FString;

typedef struct {
    FString version;
    FString build_no;
    FString build_type;
    FString build_date;
    FString build_info;
    FString comment;
} FVersionInfo;

extern "C" FAPI_EXPORT FVersionInfo CALLINGCONV fGetVersion(void);

在c#端i使用动态加载：

    [DllImport("kernel32.dll", EntryPoint = "LoadLibrary")]
    static extern int LoadLibrary(
        [MarshalAs(UnmanagedType.LPStr)] string lpLibFileName);

    [DllImport("kernel32.dll", EntryPoint = "GetProcAddress")]
    static extern IntPtr GetProcAddress(int hModule,
        [MarshalAs(UnmanagedType.LPStr)] string lpProcName);

    [DllImport("kernel32.dll", EntryPoint = "FreeLibrary")]
    static extern bool FreeLibrary(int hModule);

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    public struct FVersionInfo
    {
        public string Version;
        public string Build_No;
        public string Build_Type;
        public string Build_Date;
        public string Build_Info;
        public string Comment;
    }

    [UnmanagedFunctionPointer(CallingConvention.StdCall, CharSet = CharSet.Ansi)]
    public delegate FVersionInfo fGetVersion();

    public fGetVersion GetVersion;

    FHandle = LoadLibrary(@pName);
    IntPtr intPtr;
    intPtr = GetProcAddress(FHandle, "fGetVersion");
    GetVersion = (fGetVersion)Marshal.GetDelegateForFunctionPointer(intPtr, typeof(fGetVersion));

调用代码应该是：

FVersionInfo version = new FVersionInfo();
version = GetVersion();

我的第一个问题是，我在 c# 加载部分调用 Marshal.GetDelegateForFunctionPointer 时变成了“System.Runtime.InteropServices.MarshalDirectiveException”。

然后我使用 IntPtr 作为结构返回参数进行了测试：

[UnmanagedFunctionPointer(CallingConvention.StdCall, CharSet = CharSet.Ansi)]
public delegate IntPtr fGetVersion();

所以我让 Marshal.GetDelegateForFunctionPointer 工作，但后来我遇到了同样的编组问题：

IntPtr DllValue = new IntPtr();
FVersionInfo version = new FVersionInfo();
DllValue = fGetVersion();
Marshal.PtrToStructure(DllValue, FVersionInfo);

这里它在 fGetVersion() 调用时崩溃，并带有“托管调试助手 'PInvokeStackImbalance'”。我认为这意味着堆栈已损坏（不平衡）。

我已经测试了结构定义的许多变体，但没有结果。

欢迎任何想法或建议！

Answer 1

感谢您的指导，但我找到了一个可行的解决方案：

1. 我将结构的声明更改为

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct FVersionInfo
{
    public IntPtr Version;
    public IntPtr Build_No;
    public IntPtr Build_Type;
    public IntPtr Build_Date;
    public IntPtr Build_Info;
    public IntPtr Comment;
}

1. 所以我顺利通过了Marshal.GetDelegateForFunctionPointer。

2. 我将使用代码更改为：

GF.FVersionInfo vi = new GF.FVersionInfo();
vi = gf.GetVersion();

4. 之后，我可以访问字符串，例如使用

字符串 MyVersion = Marshal.PtrToStringAnsi(VersionInfos.Version);

Answer 2

使用带有 const char * 成员的结构的示例。在这种情况下，您可以使用自己的 C++ DLL 结构来回传递。

// CPP Source code
// ----------------------------------

// Struct definition
struct MyStruct_t {
    const char * sStr;
    size_t       iInt;
};
// ----------------------------------


// C# Source code
// ----------------------------------

// Struct definition
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]       
public struct MyStruct_t {
    public string sStr;
    public int    iInt;
};

// DLL prototype
[DllImport("Cpp.dll", CallingConvention = CallingConvention.StdCall)]
public static extern void MyFunctionCall(IntPtr MyStruct_t);

// Prepare a struct pointer to pass to DLL
MyStruct_t pMyStruct_t = new MyStruct_t();
IntPtr pMyStructPTR    = Marshal.AllocHGlobal(Marshal.SizeOf(pMyStruct_t));
Marshal.StructureToPtr(pMyStruct_t, pMyStructPTR, false);

// Call C++ DLL
MyFunctionCall(pMyStructPTR);

// The DLL updated struct, get the struct
MyStruct_t pMyStruct = (MyStruct_t)Marshal.PtrToStructure(pMyStructPTR, typeof(MyStruct_t));

// Show data
MessageBox.Show(pMyStruct.sStr);

// clean up
if (pMyStructPTR != IntPtr.Zero) { Marshal.FreeHGlobal(pMyStructPTR); pMyStructPTR = IntPtr.Zero; }
// ----------------------------------