How to change parameter in c#.

Question

Hi everone.
I have a Dll which is code by C++. And have function pointer after.
with : void GetFileList(char[] lpsz, FileInfo[] fileInfo, long* count);
with: FileInfo is struct{
char szname[256];
char pathname[256];
}FileInfo;
I use DllImport in C# to import This dll :
My code:
" [DllImport( "MyDll")]
unsafe public static extern void GetFileList(string lpsz, FileInfo [] fileInfo, long* count);
with define FileInfo in C# is struct:
public struct{
string szname;
string pathname;
}
I call GetFileList("e:\dll.zip", fileInfo, &count) ;
But I can not receive fileInfo.
fileInfo.szname = null;
with count is True.
please tell me as soon as possible .
how to receive fileInfo.
thank you.

tamnt7152004 · Answer

Thank you very much.
I not yet understand your helping.
using char[] not true. I have tried but not true.
I can use class change for struct in C#.
with:
public class FileInfo
{
private StringBuilder mszPath;
private StringBuilder mszPathReal;
public FileInfo()
{
mszPath = new StringBuilder();
mszPathReal = new StringBuilder();
}
public StringBuilder szPath
{
get
{
return mszPath;
}
set
{
this.mszPath = value;
}
}
public StringBuilder szPathReal
{
get
{
return mszPathReal;
}
set
{
this.mszPathReal = value;
}
}
}
But not true.
Thank for any help.

spgilmore · Answer

Did you write the DLL?
It's not normal for a C function to have a parameter like FileInfo[] fileinfo. That's not actually C++ syntax. C++ would say FileInfo *fileInfo. So what is the C++ prototype of the function? If it is expecting an array, a C++ array is the very same thing as a pointer to element 0 in the array, so you should probably pass &fileInfo as the second parameter.
Another thing to try is to define the C# struct using char[] instead of string. That is, afterall, closer to the C++ declaration. Second, you may try removing the UNSAFE modifier and passing just the objects, which will pass them by reference, which is the same as passing their address. It should do the same thing but you never know until you try.
BTW, there is an INTEROP section in this forum for questions about interoperability.