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Introduction
When writing ATL components, I have found that one of the hardest things for Windows
programmers to overcome is the dependency on the MFC library. For dates and strings, MFC
simplifies the programmer's job by handling memory allocations and type conversions within
its class encapsulation. However, with that simplification comes the price of having to
distribute the MFC DLL's with your component.
This article focuses on the issues surrounding the use of strings in an ATL component.
If you don't include MFC support in your ATL component, you obviously won't have
the CString available to use. There have been several articles published that address this
issue. Several of the ones that I have read are:
NonMFC:CString (posted on www.worldofatl.com) - This article provides a new
CString class based on the standard template library (STL).Add MFC's CString to ATL w/ No MFC dependencies (by K. Shane Triem
(www.codeguru.com) - This article illustrates how to use a Visual Studio macro to
extract the CString class source code from the MFC library and then use this class in your
ATL component.
CCOMString
While both of these articles are viable alternatives to the MFC CString class, I wanted
a class that would compile under both ANSI and Unicode and had no dependencies whatsoever:
neither MFC or STL. My alternative was to write a string handling class entitled
CCOMString which is based entirely on Visual C++'s TCHAR datatype.
The TCHAR datatype is defined as follows:
- As a
char when _MBCS is defined in your program.
- As a
wchar_t when _UNICODE is defined in your program.
- As a
char when neither _MBCS or _UNICODE is defined in your program.
Therefore, by using the TCHAR datatype, CCOMString is compatible with
both ANSI and Unicode compile modes. Please note
that there is one caveat to this class in its present state of development: it does
not currently include exception handling for the memory allocation functions. I am
currently trapping any memory allocation errors with the ATLASSERT macro, but these will
compile away in Release mode (I'm still researching a way to handle these errors
without adding the exception handling overhead to the class).
The current version of the CCOMString includes the following
functionality. Please note, if there are any functions in the CCOMString class that
you download that are not listed in the text below, they are considered to be undocumented
and, therefore, possibly untest as well:
Constructors
CCOMString() - Constructs an empty string.
CCOMString(CCOMString&) - Constructs a string from another CCOMString.
CCOMString(LPCTSTR) - Constructs a string from a LPCTSTR (i.e., const
TCHAR*).
CCOMString(BSTR) - Constructs a string from a BSTR.
CCOMString(TCHAR, int) - Constructs a string from a character repeated an
indicated number of times.
Assignment Operations
operator=(CCOMString&) - Copies another CCOMString object to the
CCOMString object.
operator=(LPCTSTR) - Copies a LPCTSTR to the CCOMString object.
operator=(BSTR) - Copies a BSTR to the CCOMString object.
operator LPCTSTR() - Returns a const TCHAR* from the CCOMString object.
TCHAR* GetString() - Obtains a pointer to the string contained in the
CCOMString object.
BSTR AllocSysString() - Allocates a BSTR from the CCOMString object.
Concatenation
<code>operator+=(CCOMString&) - Concatenates a CCOMString object to the end
of the CCOMString object.
operator+=(LPCTSTR) - Concatenates a const TCHAR* to the end of the
CCOMString object.
operator+=(BSTR) - Concatenates a BSTR to the end of the CCOMString object.
operator+=(TCHAR) - Concatenates a TCHAR to the end of the CCOMString
object.
operator+(CCOMString&, CCOMString&) - Concatenates two CCOMString
objects together.
operator+(CCOMString&, LPCTSTR) - Concatenates a CCOMString object and
a const TCHAR* together.
operator+(LPCTSTR, CCOMString&) - Concatenates a const TCHAR* and
CCOMString object together.
operator+(CCOMString&, BSTR) - Concatenates a CCOMString object and a
BSTR together.
operator+(BSTR, CCOMString&) - Concatenates a BSTR and a CCOMString
object together.
Accessors for the String as an Array
GetLength() - Returns the length of the CCOMString string as an integer.
IsEmpty() - Returns TRUE or FALSE depending on whether or not the
CCOMString string is empty.
Empty() - Sets the CCOMString string to an empty string (i.e.,
_T("")).
GetAt(int) - Returns a TCHAR character from the CCOMString string at the
specified location.
operator[] (int) - Same functionality as GetAt(int).
SetAt(int, TCHAR) - Sets the character at the specified location of the
CCOMString string to the specified character.
Conversions
MakeUpper() - Converts the CCOMString string into all uppercase characters.
MakeLower() - Converts the CCOMString string into all lowercase characters.
MakeReverse() - Reverses the sequence of the characters contained in the
CCOMString string.
TrimLeft() - Removes all spaces from the left-hand side of the CCOMString
string.
TrimRight() - Removes all spaces from the right-hand side of the CCOMString
string.
Searching
Find(TCHAR) - Returns the first position in the CCOMString string of the
specified character.
Find(TCHAR, int nStart) - Returns the first position after the nStart
position in the CCOMString string of the specified character.
Find(LPCTSTR lpszSub) - Returns the first position in the CCOMString string
of the specified character string.
Find(LPCTSTR lpszSub, int nStart) - Returns the first position after the
nStart position in the CCOMString string of the specified character string.
Extraction
Mid(int) - Returns a CCOMString object containing the character starting at
the specified position to the end of the CCOMString string.
Mid(int, int) - Returns a CCOMString object containing the character
starting at the specified position and extending for the specified length of the
CCOMString string.
Left(int nCount) - Returns nCount characters starting at the left-hand side
of the CCOMString string.
Right(int nCount) - Returns nCount characters starting at the right-hand
side of the CCOMString string.
Replacing
Replace(TCHAR chOld, TCHAR chNew) - Replaces all the chOld characters in
the CCOMString string with the chNew character.
Replace(LPCTSTR lpszOld, LPCTSTR lpszNew) - Replaces all the lpszOld
strings in the CCOMString string with the lpszNew string.
Comparison
Compare(CCOMString&) - Compares the current CCOMString string with the
specified CCOMString string and returns zero if equal and non-zero if not equal.
This comparision is case sensitive.
Compare(LPCTSTR) - Compares the current CCOMString string with the
specified const TCHAR* and returns zero if equal and non-zero if not equal. This
comparision is case sensitive.
operator==(const CCOMString&, const CCOMString&) - Same
functionality as Compare(CCOMString&).
operator==(const CCOMString&, LPCTSTR) - Same functionality as
Compare(LPCTSTR).
operator==(LPCTSTR, const CCOMString&) - Same functionality as
Compare(LPCTSTR).
operator!=(const CCOMString&, const CCOMString&) - Compares
the current CCOMString string with the specified CCOMString string and returns zero if not
equal and non-zero if equal. This comparision is case sensitive.
operator!=(const CCOMString&, LPCTSTR) - Compares the current
CCOMString string with the specified const TCHAR* and returns zero if not equal and
non-zero if equal.This comparision is case sensitive.
operator!=(LPCTSTR, const CCOMString&) - Same functionality as operator
!=(const CCOMString&, LPCTSTR).
CompareNoCase(CCOMString&) - Compares the current CCOMString string
with the specified CCOMString string and returns zero if equal and non-zero if not equal.
This comparision is not case sensitive.
CompareNoCase(LPCTSTR) - Compares the current CCOMString string with the
specified const TCHAR* and returns zero if equal and non-zero if not equal. This
comparision is not case sensitive.
Formatting
Format(LPCTSTR, ...) - Formats the string similar to the C function
printf().
History
28 June 2000 - memory leak fix in source
12 August 2000 - updated source ZIP file
