When C # calls C + +, the string returns a parameter with an Access exception error

C + + function prototypes:

BOOL _stdcall Psstartup (HANDLE Hprintps, LPCSTR Lpszdatabasepath, LPCSTR lpszspoolfile);

Lpszspoolfile is the return parameter, which is assigned by the Psstartup and brought back.

The first statement I made in C # was:

[DllImport ("PrintScu.dll", callingconvention = callingconvention.stdcall)]public extern static int Psstartup (INTPTR Hprintps, string lpszdatabasepath, ref string lpszspoolfile);

However, an error occurred during the actual call:

System.accessviolationexception is unhandled  message=attempted to read or write protected memory. This is often a indication that other memory is corrupt.  Source=mscorlib  StackTrace: at       System.String.. ctor (sbyte* value) at       System.StubHelpers.CSTRMarshaler.ConvertToManaged (IntPtr CStr)

After finding a circle on the internet, I found that this declaration is not possible, you cannot use ref string, and you need to use StringBuilder, and then change to the following declaration, test pass:

[DllImport ("PrintScu.dll", callingconvention = callingconvention.stdcall)]public extern static int Psstartup (INTPTR Hprintps, String lpszdatabasepath, StringBuilder lpszspoolfile);

StackOverflow Post Address

When C # calls C + +, the string returns a parameter with an Access exception error