dennismeister dennismeister - 20 days ago 6
C# Question

Aplication crashes when calling function from dll for character-set conversion

funcion on C

TCHAR* __stdcall W1251ToUtf8(CHAR* str)//функция пребразования строки из Windows-1251 в Unicode
{
int wsize = MultiByteToWideChar(CP_UTF8, 0, str, -1, NULL, 0);
TCHAR* result = new TCHAR[wsize*sizeof(TCHAR)];
MultiByteToWideChar(CP_UTF8, 0, str, -1, result, wsize);
return result;
}


function declaration in c# project

[DllImport("D://EncodingStringData.dll", EntryPoint = "W1251ToUtf8")]
static extern string W1251ToUtf8(string str);


function call

string TextForEncoding = ReadFromFile();
string OutText = W1251ToUtf8(TextForEncoding);


first time app crash without any reason, then im add try catch

try
{
string TextForEncoding = ReadFromFile();
string OutText = W1251ToUtf8(TextForEncoding);
}
catch (Win32Exception ex)
{
System.Windows.Forms.MessageBox.Show(ex.ToString());
}


and i catch accessviolationexception, now crashing againg without reason.

So anyone no what i need to do?

Answer

A few problems:

  • You pass 1251 text but ask it to be treated as UTF8. So the API function call likely fails. You don't check return value for failure.
  • Your input is 8 bit text, your output if 16 bit text, but your pinvoke assumes 8 bit for both.
  • A return value type of string leads to the returned pointer being passed CoTaskMemFree for deallocation.

The exit code is STATUS_HEAP_CORRUPTION which suggests the final bullet is the immediate problem. Fix that by returning IntPtr and convert to text with Marshal.PtrToStringUni. And also export a deallocator. Or allocate off a shared heap. Or return a COM BStr. Indeed use any of the correct ways to return a string.

Having fixed that problem you'll need to fix the others too.

Quite why you won't use System.Text.Encoding is beyond me.

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