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[VictorN]

... Note that WriteString does not add the end of line characters, so you would nee to do it yourself when you need it:

CString str = _T("String to write\r\n");
file.WriteString(str);

This code is not 100% correct.
you should NOT add CR ('\r') character yourself, only LF ('\n'). CStdioFile::WriteString will then replace

... any newline character ... written to the file as a carriage return–linefeed pair.

So, the correct code is:

CString str = _T("String to write\n");
file.WriteString(str);