Thread: CFile::Write() problem

Hi

Code:

...
m_cfile.Open(m_txtfilepath, CFile::modeCreate|CFile::modeWrite, NULL);
UpdateData(TRUE);
m_cfile.Write(m_remain, m_remain.GetLength());
...

Above code opens a file and write some data which are in a Edit box (RichEdit) into the file. m_remain is the CString variable which has bind to the Edit box. Problem is that when i write to the file, only the first few chars in the Edit box is written to the file. No problem with m_remain coz when i debug, m_remain shows what's in the edit box correctly. Whatz happening here? Some help please.

Thanx.

Did that. But still it writes only first 4 chars. im using VS 2005.
?

Yes. For example if the edit box contains "CProgramming", then the output would be something like "CPro".

GetLength() returns the number of characters.
Write() expects number of bytes.
1 char = 1 byte
1 wchar_t = 2 bytes

If for your project, TCHAR = wchar_t, then you're only writing half the number of bytes you should.

Cast to "LPCSTR" if you're intention is to write a simple ansi text file.

gg

Thanx that worked! i did

Code:

 m_remain.GetLength() * 2)

and it worked. Though casting to LPCSTR gave an error.

Another problem. After i write the data, i need to read it back. i did,

Code:

..
CFile m_cfile;
char m_txtdata[100000] = "\0";
m_cfile.Open(m_txtfilepath,CFile::modeRead,NULL);
m_cfile.Read(m_txtdata, 10000);
..

But the Read function only reads the 1st char of the file now. For example, if i write "Boolean" using the code in previous question, Read() only reads "B". But when i try read a text file which isn't written by this program, it reads the entire file correctly. Why is that?
Thx.

>> return (wcslen(Str) * sizeof(TCHAR)) + sizeof(TCHAR);
You should use _tcs[c]len() to get the length of a TCHAR string.

Writing TCHAR's to a file doesn't really make sense, unless you really intend to tie the format/encoding of the file to your project settings.

>> But the Read function only reads the 1st char of the file now.
It's reading more, you just don't "see" it because every other byte is 0. You wrote wchar_t's, and are reading char's.

Just write and read char's:

Code:

CStringA ansi_str = m_remain;
// write ansi_str

gg

>> ... MSDN says that GetLenght() returns the number of bytes.
Yeah, that's bad VS 6.0 documentation. But they did get it right in one spot:
http://msdn.microsoft.com/en-us/libr...8VS.60%29.aspx

VS 2005 Docs: http://msdn.microsoft.com/en-us/libr...8VS.80%29.aspx

gg

Originally Posted by Codeplug

GetLength() returns the number of characters.
Write() expects number of bytes.

"Number of characters" isn't even accurate. It should be "number of CHAR's or number of WCHAR's".

A multi-byte codepage can have several bytes per "glyph", and a Unicode grapheme (jargon for glyph) can be made up of more than one code-point. And since Windows uses UTF16LE encoding (WCHAR = 2-bytes), there can be more than one WCHAR per code-point.

>> You should use _tcs[c]len() to get the length of a TCHAR string
Using _tcsclen() would be a mistake, since that can map to _mbslen(), which doesn't necessarily return the number of char's/bytes, as intended.

gg