Marshaling Complex Structs

So Microsoft has done a great deal to help with interop but sometimes it gets tricky. For instance, last week I was trying to call a C++ function which expected a semi-complex struct as its parameter... typedef struct {   int serial_number;   struct in_addr ip_address;   time_t oldestfile[MAXDRDCHANNELS];   time_t newestfile[MAXDRDCHANNELS];   int group[MAXDRDCHANNELS];   char groupname[MAXDRDCHANNELS][NAMELENGTH];   char commonname[MAXDRDCHANNELS][NAMELENGTH]; } foo; After crunching away for a while, the solution was... private struct Foo {   int serialNumber;   int ipAddress;   int oldestFile0;   int oldestFile1;   int oldestFile2;   int oldestFile3;   int newestFile0;   int newestFile1;   int newestFile2;   int newestFile3;   int group0;   int group1;   int group2;   int group3;   [MarshalAs(UnmanagedType.ByValArray, ArraySubType=UnmanagedType.U1, SizeConst=21)] char groupName0;   [MarshalAs(UnmanagedType.ByValArray, ArraySubType=UnmanagedType.U1, SizeConst=21)] char groupName1;   [MarshalAs(UnmanagedType.ByValArray, ArraySubType=UnmanagedType.U1, SizeConst=21)] char groupName2;   [MarshalAs(UnmanagedType.ByValArray, ArraySubType=UnmanagedType.U1, SizeConst=21)] char groupName3;   [MarshalAs(UnmanagedType.ByValArray, ArraySubType=UnmanagedType.U1, SizeConst=21)] char commonName0;   [MarshalAs(UnmanagedType.ByValArray, ArraySubType=UnmanagedType.U1, SizeConst=21)] char commonName1;   [MarshalAs(UnmanagedType.ByValArray, ArraySubType=UnmanagedType.U1, SizeConst=21)] char commonName2;   [MarshalAs(UnmanagedType.ByValArray, ArraySubType=UnmanagedType.U1, SizeConst=21)] char commonName3; } In this case, I knew the array members of the struct were only ever going to contain 4 elements, so I just had to pass them in as individual variables. Things got tricky when I was trying to marshal a C++ char array. You can see by setting the above attribute on the char with an explicit size and type, I got away with it.