从c#应用程序调用c++ DLL

Call a C++ DLL from a C# application

本文关键字：c++ DLL 调用 应用程序      更新时间：2023-10-16

我目前正在尝试将c++ DLL集成到我们的c#应用程序中，但我无法确定调用其中一个方法的正确方式。在文档的两个不同地方，方法定义是不相等的:

ImageAndScanError GetMicrInfo(unsigned char *ptrCodeline,int* iLength) 
ImageAndScanError WINAPI GetMicrInfo(char* cMicrInfo,int* iInfoLength);
/*
ImageAndScanError GetMicrInfo(unsigned char *ptrCodeline,int* iLength) 
Parameters: 
ptrCodeline: a pointer to the output buffer that will receive the code line read by the MICR algorithm. The ptrCodeline should allocate room for 96 characters. 
iLength: the number of characters contained in the code line 
Function: Read MICR line on the check. This function must be called after StartScan . 
Returns: ErrorNone is returned upon success. Otherwise, an enum ImageAndScanError value that indicates the reason for failure is returned. 
*/
这就是我如何包含dll方法 
[DllImport("ScanDll.dll", CallingConvention = CallingConvention.Winapi)]

这是目前为止我做过的所有组合

public static extern ImageAndScanError GetMicrInfo(out IntPtr cMicrInfo, out int iInfoLength);
public static extern ImageAndScanError GetMicrInfo(out byte[] cMicrInfo, out int iInfoLength);
public static extern ImageAndScanError GetMicrInfo(out string cMicrInfo, out int iInfoLength);
public static extern ImageAndScanError GetMicrInfo(out StringBuilder cMicrInfo, out int iInfoLength);
IntPtr cMicrInfoTMP;
byte[] cMicrInfoTMP= new byte[96];
string cMicrInfoTMP;
StringBuilder cMicrInfoTMP;
GetMicrInfo(out cMicrInfoTMP, out iInfoLengthTMP);

当我使用IntPtr时，在VS2010中调试给我的值是859256727，大小为4，当我执行

时
string myString = Marshal.PtrToStringAnsi(cMicrInfoTMP);

我总是得到一个空字符串

当我尝试任何其他(byte[]， string, StringBuilder)时，我得到

The runtime has encountered a fatal error. The address of the error was at
0x53e6716a, on thread 0x1084. The error code is 0xc0000005. This error may
be a bug in the CLR or in the unsafe or non-verifiable portions of user
code. Common sources of this bug include user marshaling errors for COM-interop
or PInvoke, which may corrupt the stack.

我在这里错过了什么?由于

您可以分配一个缓冲区，然后传递给本机函数。

//error handling omitted
[DllImport("your.dll", CharSet = CharSet.Ansi)]
ImageAndScanError GetMicrInfo(IntPtr ptrCodeline,ref int bytesCopied);
IntPtr ip = Marshal.AllocCoTaskMem(bufferLen);
Win32API.ZeroMemory(ip, (uint)(bufferLen));
int bytesCopied=0;
GetMicrInfo(ip, ref bytesCopied);
string info= Marshal.PtrToStringAnsi(bytesCopied);
Marshal.FreeCoTaskMem(ip);

如果您不需要在多次调用GetMicrInfo期间重用缓冲区，您可以使用StringBuilder的默认封送器:

[DllImport("your.dll", CharSet = CharSet.Ansi)]
ImageAndScanError GetMicrInfo(StringBuilder ptrCodeline,ref int bytesCopied);
StringBuilder ptrCodeline(bufferLen);
int bytesCopied=0;
GetMicrInfo(ptrCodeline, ref bytesCopied);

如果多次调用GetMicrInfo，它会带来性能损失，因为在每次调用时，默认的CLR编组器都会创建一个用于固定和unicode-ANSI转换的编组缓冲区。如果函数不经常被调用或不返回大量数据，则此命中可以忽略不计。

参考:

  • 字符串默认封送处理
  • 托管和非托管代码之间的封送处理

在。net中，当被调用者创建对象时使用out参数。您需要为函数提供一个现有的缓冲区，因此应该首先初始化StringBuilder。然后，编组程序将指向对象的内部字符缓冲区的指针传递给函数。

您必须弄清楚MICR字符串使用的是哪个字符集和编码。它可以是UTF-16，在这种情况下，将声明更改为CharSet.Unicode。

试试这个:

[DllImport("ScanDll.dll", CallingConvention = CallingConvention.Winapi, CharSet = CharSet.Ansi)]
private static extern ImageAndScanError GetMicrInfo(StringBuilder cMicrInfo, out int iInfoLength);
public String GetMicrInfo()
{
    StringBuilder info = new StringBuilder(96);
    int length;
    ImageAndScanError error = GetMicrInfo(info, out length);
    if (error != ImageAndScanError.ErrorNone) throw new Exception(String.Format("GetMicrInfo error: {0}", error));
    return info.ToString();
}

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