从C＃应用程序调用C++ DLL

Question

我正在尝试将C++ DLL集成到我们的C＃应用​​程序中，但我无法确定调用其方法之一的正确方法。在文件的两个不同地方的方法定义不相等：

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. 
*/ 

这是我多么包括dll方法

[DllImport("ScanDll.dll", CallingConvention = CallingConvention.Winapi)] 

这是我做了这样所有组合远

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); 

当我使用的IntPtr，使得调试让我在VS2010是859256727大小为4，和值，当我做

string myString = Marshal.PtrToStringAnsi(cMicrInfoTMP); 

我总是得到一个空字符串。

当我尝试任何其他人（字节[]，字符串，StringBuilder的）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. 

缺少什么我在这里？ 谢谢

Answer 1

您可以分配一个缓冲区，然后传递到本地功能。

//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); 

如果您不需要再使用时GetMicrInfo的多个调用缓存，您可以使用StringBuilder的默认封送：

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

它配备了一个性能命中，如果你打电话GetMicrInfo多次，因为在每次调用时，默认的CLR编组器会创建一个封送缓冲区以用于锁定和unicode-ANSI转换。如果该函数没有被频繁调用或者不返回大量数据，则该命中可能可以忽略不计。

参考：

• Default Marshaling for Strings
• Marshaling between Managed and Unmanaged Code

Answer 2

在.NET中，out参数用于被调用者创建对象时。你需要为函数提供一个现有的缓冲区，所以你应该首先初始化StringBuilder。编组器然后将一个指针传递给对象的内部字符缓冲区到函数。

您必须弄清楚MICR字符串正在使用哪种字符集和编码。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(); 
}