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

Question

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 know what i need to do?

This function is bananas. The name and comment imply it converts Windows-1251 characters into UTF-8, which is not at all what it does -- it converts UTF-8 to UTF-16. Regardless of what it does or is supposed to do, there's a perfectly safe managed equivalent that does not require calling it at all. Use `System.Text.Encoding` to convert between encodings and don't bother with this. — Jeroen Mostert, Nov 13 '16 at 23:06
Jeroen is right. See [this question](http://stackoverflow.com/questions/14057434/how-can-i-transform-string-to-utf-8-in-c) for some sample code — NineBerry, Nov 13 '16 at 23:09
@Abion47 program has exited with code -1073740940 (0xc0000374). — dennismeister, Nov 13 '16 at 23:49
That exit code doesn't tell me much of anything at all. Rather than Google it, though, I will reiterate what others have said. There is a much simpler and safer method of doing exactly this without having to bother with C code or P/Invokes, and insisting on this method after knowing that is clinically insane. — Abion47, Nov 13 '16 at 23:56

David Heffernan · Accepted Answer · 2016-11-14T08:07:59.247

1

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.

edited Nov 14 '16 at 08:07

answered Nov 14 '16 at 07:59

David Heffernan

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i dont use c# tool coz my project name is "using win32/64 api dll in c# project" – dennismeister Nov 14 '16 at 08:54
what i need to do with another construction Declaration on C CHAR* __stdcall Utf8ToW1251(TCHAR* str); Wich types i need to use in C# code? private static extern string Utf8ToW1251(IntPtr str); IntPtr TextForEncodingInInt = Marshal.StringToHGlobalUni (TextForEncoding); string OutText = Utf8ToW1251(TextForEncodingInInt); its didnt work – dennismeister Nov 20 '16 at 20:38
Well no. You'll need to encode the UTF8 manually. And your function will need to deallocation the returned value too. – David Heffernan Nov 20 '16 at 20:41
so i need to put into function string and take IntPtr? – dennismeister Nov 21 '16 at 00:53
This is a different question. – David Heffernan Nov 21 '16 at 05:02

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

1 Answers1