c# - Marshaling CTL_USAGE -

i'm doing project work certificates , need convert ctl_usage structure c#. original structure follows:

typedef struct _ctl_usage {   dword cusageidentifier;   lpstr *rgpszusageidentifier; } ctl_usage, *pctl_usage, cert_enhkey_usage, *pcert_enhkey_usage; 

according p/invoke website, c# structure should this:

[structlayout(layoutkind.sequential)] public struct ctl_usage {     public int cusageidentifier;     public intptr rgpszusageidentifier; } 

to use code, convert each string want add structure byte array using encoding.ascii.getbytes(). turn byte array gchandle using gchandle.alloc(bytearray, gchandletype.pinned). add value array of intptrs , create gchandle intptr array , assign rgpszusageidentifier. call cryptencodeobjectex doesn't throw error, resulting data garbage , cannot unencrypted using cryptdecodeobject. encoding follows:

//enhancedusage list<string> containing enhanced usage oids ctl_usage usage = new ctl_usage() {     cusageidentifier = enhancedusage.count, };  list<intptr> usagelist = new list<intptr>();  foreach (string s in enhancedusage)     usagelist.add(new pinnedhandle(encoding.ascii.getbytes(s)));  usage.rgpszusageidentifier = new pinnedhandle(usagelist.toarray());  intptr data = marshal.allochglobal(marshal.sizeof(usage)); marshal.structuretoptr(usage, data, false);  int encodedsize = 0;  if (!crypt32.cryptencodeobjectex((int)certencoding.x509asn, certoid.szoid_enhanced_key_usage, data, 0, intptr.zero, null, ref encodedsize))     throw new win32exception();  byte[] buffer = new byte[encodedsize];  if (!crypt32.cryptencodeobjectex((int)certencoding.x509asn, certoid.szoid_enhanced_key_usage, data, 0, intptr.zero, buffer, ref encodedsize))     throw new win32exception(); 

the pinnedhandle class wrapper gchandle. looks this:

public class pinnedhandle : idisposable {     private gchandle handle;      public pinnedhandle(object value)     {         handle = gchandle.alloc(value, gchandletype.pinned);     }      public static implicit operator intptr(pinnedhandle value)     {         return value.handle.addrofpinnedobject();     }      public void dispose()     {         try         {             handle.free();         }         catch         {          }     } } 

i don't think it's causing problem here i've used in other similar situations , they're working properly. idea how make work correctly?

allocate unmanaged memory block allochglobal, copy intptr instances usagelist it, , pass block handle unmanaged function. use marshal.writeintptr method (intptr, int32, intptr) this.

http://msdn.microsoft.com/en-us/library/ms146679.aspx

in interoperability code avoid pinning managed objects , prefer build native memory regions, using different marshal methods.