如何为P/Invoke声明指向结构的指针

本文关键字：结构 指针 声明 Invoke | 更新日期: 2023-09-27 18:26:22

我正在尝试使用p/Invoke Interop Assistant来调用C#中的C++Dll。大部分标题都转换得很好，但我遇到了问题：

#define FULLOCTAVE_BINS                12
#define THIRDOCTAVE_BINS               36
typedef struct tagTimeHistory
{
    UINT m_nAction;
    int m_nFlag;
    int m_nRecordNum; 
    int m_nTimeStamp;
    int m_nMiscStartIndex;
    float m_pfTHFloatVals[256]; // Number of valid values given by m_nNumFloatVals in Settings.
    float m_pfTH11OBAVals[4][FULLOCTAVE_BINS];  // 0-4 spectra given by m_nNumOBA11Vals in Settings
    float m_pfTH13OBAVals[4][THIRDOCTAVE_BINS]; // 0-4 spectra given by m_nNumOBA13Vals in Settings
    float m_fDuration;
} stTimeHistory_t;
typedef struct tagSlmBulkRecords
{
    int nRecType;
    union
    {
        stTimeHistory_t *m_ThRecs;
        stInterval_t    *m_Interval;
        stExceedence_t  *m_Exceedences;
        stRunRecord_t   *m_RunRecord;
        stSpeechData_t  *m_VoiceRecord;
        stSpeechData_t  *m_AudioRecord;
    };
} stSlmBulkRecord_t;

这被转换为：

[System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Explicit)]
public struct Anonymous_d2bf9406_c664_4664_9196_800cc23f445a {
    /// stTimeHistory_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr m_ThRecs;
    /// stInterval_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr m_Interval;
    /// stExceedence_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr m_Exceedences;
    /// stRunRecord_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr m_RunRecord;
    /// stSpeechData_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr m_VoiceRecord;
    /// stSpeechData_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr m_AudioRecord;
}
[System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
public struct tagSlmBulkRecords {
    /// int
    public int nRecType;
    /// Anonymous_d2bf9406_c664_4664_9196_800cc23f445a
    public Anonymous_d2bf9406_c664_4664_9196_800cc23f445a Union1;
}

但是，当m_ThRecs只是System.IntPtr时，我如何使用它？是否有某种方法可以显式地将其声明为指向stTimeHistory_t的指针？我移植到C#的C++代码是这样使用的：

stSlmBulkRecord_t   bulkRecord;
bulkRecord.m_ThRecs = new stTimeHistory_t[dataCounts.m_nNumTH];

但是如果我在C#中尝试这个：

tagSlmBulkRecords bulkRecord;
bulkRecord.Union1.m_ThRecs = new tagTimeHistory[dataCounts.m_nNumTH];

我得到：

错误1无法将类型"SlmTest.Program.tagTimeHistory[]"隐式转换为"SlmTest.Program.tagTimeHistory"

如果我尝试一个不安全的定义：

[System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
public struct tagTimeHistory
{
    /// UINT->unsigned int
    public uint m_nAction;
    /// int
    public int m_nFlag;
    /// int
    public int m_nRecordNum;
    /// int
    public int m_nTimeStamp;
    /// int
    public int m_nMiscStartIndex;
    /// float[256]
    [System.Runtime.InteropServices.MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst = 256, ArraySubType = System.Runtime.InteropServices.UnmanagedType.R4)]
    public float[] m_pfTHFloatVals;
    /// float[48]
    [System.Runtime.InteropServices.MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst = 48, ArraySubType = System.Runtime.InteropServices.UnmanagedType.R4)]
    public float[] m_pfTH11OBAVals;
    /// float[144]
    [System.Runtime.InteropServices.MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst = 144, ArraySubType = System.Runtime.InteropServices.UnmanagedType.R4)]
    public float[] m_pfTH13OBAVals;
    /// float
    public float m_fDuration;
}
[System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Explicit)]
public unsafe struct Anonymous_d2bf9406_c664_4664_9196_800cc23f445a
{
    /// stTimeHistory_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public tagTimeHistory *m_ThRecs;
    /// stInterval_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr *m_Interval;
    /// stExceedence_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr m_Exceedences;
    /// stRunRecord_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr m_RunRecord;
    /// stSpeechData_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr m_VoiceRecord;
    /// stSpeechData_t*
    [System.Runtime.InteropServices.FieldOffsetAttribute(0)]
    public System.IntPtr m_AudioRecord;
}

我得到：

错误CS0208:无法获取的地址、获取的大小或声明指向托管类型的指针

如何为P/Invoke声明指向结构的指针

如果真的想与本机代码进行互操作，可以使用fixed运算符：

var array = new tagTimeHistory[dataCounts.m_nNumTH];
fixed (tagTimeHistory* ptr = array)
{
    // do anything with the raw pointer
}

请注意，C#中的fixed运算符和指针类型需要unsafe功能。您可能希望用正确的指针类型替换IntPtrs，以提高类型安全性（尽管有一种方法可以将指针转换为IntPtrs并返回）。

另一种相同的方法是通过Marshal类的方法。

编辑这是一个修改后的不安全定义的示例，该定义是您有趣的命名联合结构：

[StructLayout(LayoutKind.Explicit)]
public unsafe struct Anonymous_d2bf9406_c664_4664_9196_800cc23f445a
{
    [FieldOffset(0)]
    public stTimeHistory_t* m_ThRecs;
    [FieldOffset(0)]
    public stInterval_t* m_Interval;
    [FieldOffset(0)]
    public stExceedence_t* m_Exceedences;
    [FieldOffset(0)]
    public stRunRecord_t* m_RunRecord;
    [FieldOffset(0)]
    public stSpeechData_t* m_VoiceRecord;
    [FieldOffset(0)]
    public stSpeechData_t* m_AudioRecord;
}

您应该在代码中定义所有结构，如stTimeHistory_t（或者用通用IntPtr替换您不关心的结构）。

关于用Marshal创建结构数组：本地内存池没有structure array这样的概念；它所关心的只是字节。因此，例如，您可以使用Marshal.AllocHGlobal方法：

IntPtr myPtr = Marshal.AllocHGlobal(Marshal.SizeOf<tagTimeHistory>() * dataCounts.m_nNumTH);
// ... write something to an array, use it
// And don't forget to free it to prevent memory leaks!
Marshal.FreeHGlobal(myPtr);

EDIT 2.关于"无法获取的地址、获取的大小或声明指向托管类型的指针"错误，您的定义不是完全非托管的。不安全的定义和使用封送处理逻辑的定义并不总是相等的；在这里，它认为你的类是"托管的"，因为其中有数组引用。试试固定数组：

[StructLayout(LayoutKind.Sequential)]
public unsafe struct tagTimeHistory
{
    public uint m_nAction;
    public int m_nFlag;
    public int m_nRecordNum;
    public int m_nTimeStamp;
    public int m_nMiscStartIndex;
    public fixed float m_pfTHFloatVals[256];
    public fixed float m_pfTH11OBAVals[48];
    public fixed float m_pfTH13OBAVals[144];
    public float m_fDuration;
}
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