C#调用C++ 平台调用P/Invoke 结构体--内存对齐方式、union封装【七】

【1】内存对齐方式

C++代码：

#pragma pack(push)
#pragma pack(1)
typedef struct _testStru2
{
  int   iVal;
  char  cVal;
  __int64 llVal;
}testStru2;
#pragma pack(pop)

EXPORTDLL_API void Struct_PackN( testStru2 *pStru )
{
  if (NULL == pStru)
  {
    return;
  }

  pStru->iVal = 1;
  pStru->cVal = 'a';
  pStru->llVal = 2;

  wprintf(L"Struct_PackN \n");
}

C#代码，指定Pack即可：

[StructLayout(LayoutKind.Sequential, Pack = 1, CharSet = CharSet.Unicode)]
public struct testStru2
{
    public int   iVal;
    public sbyte cVal;
    public long  llVal;
};
[DllImport("ExportDll.dll", CharSet = CharSet.Unicode)]
public static extern void Struct_PackN(ref testStru2 pStru);

测试：

CExportDll.testStru2 stru2 = new CExportDll.testStru2();
CExportDll.Struct_PackN(ref stru2);

【2】Union中含有结构体

C++代码：

typedef union _testStru4
{
  int   iValLower;
  int   iValUpper;
  struct 
  {
    __int64 llLocation;
  };
}testStru4;

EXPORTDLL_API void Struct_Union( testStru4 *pStru )
{
  if (NULL == pStru)
  {
    return;
  }
  
  pStru->llLocation = 1024;
  wprintf(L"Struct_Union \n");
}

C#代码：定义成Explict，并显示通过FieldOffset指定内存偏移

[StructLayout(LayoutKind.Explicit, CharSet=CharSet.Unicode)]
public struct testStru4
{
    [FieldOffset(0)]
    int     iValLower;
    [FieldOffset(4)]
    int     iValUpper;
    [FieldOffset(0)]       
    long    llLocation;         
};
[DllImport("ExportDll.dll", CharSet = CharSet.Unicode)]
public static extern void Struct_Union(ref testStru4 pStru);

测试：

CExportDll.testStru4 stru4 = new CExportDll.testStru4();
CExportDll.Struct_Union(ref stru4);