Can WriteFile() be used to write wchar_t characters to a file?

Question

I am trying to write a string of type wchar_t to a file using WriteFile(). Here is the code:

void main()
{
  wchar_t dataString[1024];

  HANDLE hEvent, hFile;
  DWORD dwBytesWritten, dwBytesToWrite;

  hFile = CreateFileW(L"e:\\test.txt", GENERIC_WRITE | GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

  if(hFile == INVALID_HANDLE_VALUE)
  {
     printf("Invalid file handle: %d\n", GetLastError());
     return;
  }

  wcscpy(dataString, L"Hello");
  dwBytesToWrite = wcslen(dataString);
  WriteFile(hFile, (LPVOID )dataString, dwBytesToWrite, &dwBytesWritten, NULL);

  CloseHandle(hFile);

}

I expect the string Hello to be written to the file. However the output inside the file is like this:

H e l

Any idea why it is not writing the entire string Hello to the file?

score 2 · Accepted Answer · answered May 31 '16 at 06:57

dwBytesToWrite = wcslen(dataString);

does not return the number of bytes but the number of characters. As you use wide characters (2 bytes per character), only some of them will be written to the file.

Try this instead:

dwBytesToWrite = wcslen(dataString) * sizeof(wchar_t);

score 0 · Answer 2 · edited Jun 18 '16 at 09:32

add Byte order mark (see: https://en.wikipedia.org/wiki/Byte_order_mark)(UTF-8(0xEF,0xBB,0xBF)) at the begining of text file
convert the string to UTF-8 encoding(https://en.wikipedia.org/wiki/UTF-8).

try following

/////////////        
{
unsigned char utf8BOM[3]={0xef,0xbb,0xbf};
unsigned int i=0;
DWORD bytesWrote;
unsigned int stringLen=wcslen(dataString);
WriteFile(hFile,utf8BOM,3,&bytesWrote,0);
unsigned int i=0;
while(i< stringLen){

    unsigned char buf3[3];
    if(((unsigned short)dataString[i])>0x7FF){
        buf3[0]=(0xe0 | (0x0F & (dataString[i]>>12)));
        buf3[1]=(0x80 | (0x03F & (dataString[i]>>6)));
        buf3[2]=(0x80 | (0x03F & (dataString[i])));
        WriteFile(hFile,buf3,3,&bytesWrote,0);
    }
    else{
        if(((unsigned short)dataString[i]) > 0x7F){
            buf3[0]=((dataString[i]>>6)&0x03) | 0xC0;
            buf3[1]=(dataString[i] & 0x3F) | 0x80;
            WriteFile(hFile,buf3,2,&bytesWrote,0);
        }
        else{
            buf3[0]=dataString[i];
            WriteFile(hFile,buf3,1,&bytesWrote,0);
        }
    }

    i++;
}
}
////////////////////

Can WriteFile() be used to write wchar_t characters to a file?

2 Answers2