Question

I am trying to get simple file IO working in Win32. So far the writing is working fine, but the reading is not: although it successfully reads the contents, additional “garbage” is appended to the string. The code I have so far is below. The program has UNICODE defined.

For writing:

DWORD dwTextSize = GetWindowTextLength(hWndTextBox);
WCHAR *lpszText = new WCHAR[dwTextSize];
GetWindowText(hWndTextBox, lpszText, dwTextSize + 1);
hTextFile = CreateFile(lpszTextFileName, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
DWORD dwBytesWritten;
WriteFile(hTextFile, lpszText, 2 * dwTextSize, &dwBytesWritten, NULL);  // x2 for 2 bytes per Unicode character
CloseHandle(hTextFile);
DeleteObject(hTextFile);

For this example, Hello, World! is saved successfully as Hello, World!.

For reading:

lpszTextFileName = L"text.txt";        // LPCTSTR Variable
hTextFile = CreateFile(lpszTextFileName, GENERIC_READ, 0, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
DWORD dwFileSize = GetFileSize(hTextFile, &dwFileSize);
DWORD dwBytesRead;
WCHAR *lpszText = new WCHAR[dwFileSize / 2];
ReadFile(hTextFile, lpszText, dwFileSize, &dwBytesRead, NULL);
CloseHandle(hTextFile);

The string is then used to set the text of an EDIT control:

SendMessage(hWndTextBox, WM_SETTEXT, NULL, (LPARAM)lpszText);    // SetWindowText() also possible

When Hello, World! is read back in, it reads back in as Hello, World!﷽﷽ꮫꮫꮫꮫﻮ or a visual variation upon this, but basically “garbage”!

I have probably missed something rather obvious, but I cannot see where! Is there a solution to this problem and if so, what is it?

Answer 1

Ok I started this with a comment, but its getting out of control.

For Writing

This:

WCHAR *lpszText = new WCHAR[dwTextSize];

should be:

WCHAR *lpszText = new WCHAR[dwTextSize+1];

This:

DeleteObject(hTextFile);

should not be there at all.. Get rid of it.

I’m assuming you delete [] lpszText; somewhere when you’re done with it. if not, do so.

---

For Reading

The second parameter to GetFileSize() should not be the same variable as your return value. It is the HIGH 32bit of a 64-bit value for large file sizes. If you know you’re file size is smaller than 4gB, you can leave it NULL, so change this:

DWORD dwFileSize = GetFileSize(hTextFile, &dwFileSize);

to this:

DWORD dwFileSize = GetFileSize(hTextFile, NULL);

You must account for the null terminator of your file buffer, so this:

WCHAR *lpszText = new WCHAR[dwFileSize / 2];

should be changed to this:

WCHAR *lpszText = new WCHAR[dwFileSize / 2 + 1];
lpszText[dwFileSize / 2] = 0;

and the rest should work as you’re hoping it would. No error checking, which is not good, but I’ve seen worse. And as before, I’m assuming you delete [] lpszText; somewhere when you’re done with it. if not, do so.