c# - 使用多个指针在 C# 中编码 native .dll

Question

在 C++ 中具有以下代码:

• nConId is Connection Identifier
• pParName the parameter name
• pSubName the subParameter Name (if any)
• pValue_out a pointer to a char array of lenght FCL_PAR_VALUE_LENGH
• nValueSize the real size of pValue_out vector (at least FCL_PAR_VALUE_LENGH)

extern "C" MY_API int ReadParameter(const ConnectionId_T nConId, const char* pParName,
    const char *pSubName, char *pValue_out, const int nValueSize );

我的尝试是:

[DllImport("mydll.dll", CharSet = CharSet.Ansi,CallingConvention=CallingConvention.Cdecl)]
public static extern int ReadParameter(ConnectionId_T pConId, IntPtr pParName,
    ref IntPtr pSubName, ref IntPtr[] pValue_out, int nValueSize);

我使用以下代码来调用该函数:

# nConId is returned from another function and the his value is 0

public const int FCL_PAR_VALUE_LENGH = 128; 

string param_string = "AUXF";
IntPtr pParName = (IntPtr)Marshal.StringToHGlobalAnsi(param_string);

string subparam_string = "T";
IntPtr pSubName = (IntPtr)Marshal.StringToHGlobalAnsi(subparam_string);

IntPtr[] aParValue = new IntPtr[FCL_PAR_VALUE_LENGH]; 

int returnedValue = ReadParameter(nConId, pParName, ref pSubName,
    ref aParValue, FCL_PAR_VALUE_LENGH);

当我运行代码时，我得到一个AccessViolationException，所以我猜我的调用有问题。

我的编码(marshal)错了吗？为了获得良好的响应，我必须在代码中更改哪些内容？

PS:我也知道该调用还会向 aParValue 返回一些内容。

Answer 1

您对这些 char* 的工作太辛苦了。将 System.String 编码用于输入，并编码 StringBuilder 用于输出是完全合法(并鼓励)的。

[DllImport("mydll.dll", CharSet = CharSet.Ansi,CallingConvention=CallingConvention.Cdecl)]
public static extern int ReadParameter(
    ConnectionId_T pConId, 
    string pParName, 
    string pSubName,
    StringBuilder pValue_out,
    int nValueSize);

使用

const int sbLength = 256; //use a domain relevant value
StringBuilder sb = new StringBuilder(sbLength + 1); //for null character, hard to say if you need it without seeing the C++ code, but easier to just add it than find out.
int result = ReadParameter(conId, "paramname", "paramsubname", sb, sbLength);

您没有给出有关 ConnectionId_T 基础类型的任何指示，因此我假设您已排除该问题。

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