Re: exceptions in constructor

From:

"Peter" <junk189973@sbcglobal.net>

Newsgroups:

comp.lang.c++

Date:

Sun, 19 Oct 2008 19:37:43 -0700

Message-ID:

<%9SKk.5885$YU2.5801@nlpi066.nbdc.sbc.com>

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<vaclavpich@atlas.cz> wrote in message =
news:a86624e5-ceef-4c5c-a369-21f67fb935e4@d31g2000hsg.googlegroups.com...=

CObject::CObject()
{
// 1) if ( FAILED( LoadLibrary(...) )) throw exception1;

// 2) if ( FAILED(CoInitialize( 0 )) throw exception2;

// 3) if ( FAILED( CoCreateInstance(....))) throw exception3;
}

CObject::~CObject()
{
// 1) release COM interface

// 2) CoUninitialize();

// 2) FreeLibrary
}

you should put the separate objects (HANDLE returned by LoadLibrary, =
CoInitialize()/CoUninitialize() and CoCreateInstance()) into separate =
classes and combine these classes into base-class or member-class =
relationships.
Doing it this way you don't have to clean up yourself anymore but rely =
on the code generation features of the compiler. And you can reuse these =
classes next time you're calling these functions.
And the caller of you'r code will get rich error information.

class CPLoadLibrary
{ private:
HINSTANCE h;
public:
inline CPLoadLibrary(const _TCHAR *pName)
{ if (!(h = LoadLibrary(pName)))
   throwSystemException(
       GetLastError(),
       CString(_T("LoadLibrary(\"")) + CString(pName) + =
CString(_T("\")")));
}
inline ~CPLoadLibrary(void)
{ FreeLibrary(h);
}
inline void *getProcAddress(const char *pName)
{ void *p;

  if (!(p = ::GetProcAddress(h, pName)))
   throwSystemException(
       GetLastError(),
       _T("GetProcAddress()"));
  return p;
}
inline operator HINSTANCE (void)
{ return h;
}
inline HINSTANCE getHINSTANCE(void)
{ return h;
}
};

template<class T, const IID *_piREFIID>
class CPCoCreateInstance
{ private:
T *m_p;
public:
inline CPCoCreateInstance(
     REFCLSID _iCLSID,
     IUnknown *_pUnkOuter,
     DWORD _iClsContext)
{ HRESULT iRet;

  m_p = 0;
  if (FAILED(iRet = CoCreateInstance(_iCLSID, _pUnkOuter, =
_iClsContext, *_piREFIID, (void**)&m_p)))
   throwSystemException(iRet, _T("CoCreateInstance()"));
  if (!m_p)
   throwSystemException(E_FAIL, _T("CoCreateInstance()"));
}
inline ~CPCoCreateInstance(void)
{ if (m_p)
   m_p->Release();
}
inline operator T *(void)
{ return m_p;
}
inline T *getPtr(void)
{ return m_p;
}
inline T *detach(void)
{ T *pRet = m_p;
  m_p = 0;
  return pRet;
}
};

class CPCoInitializeEx
{ private:
public:
inline CPCoInitializeEx(void *_pReserved, DWORD _iFlags)
{ HRESULT iRet;

  if (FAILED(iRet = CoInitializeEx(_pReserved, _iFlags)))
   throwSystemException(iRet, _T("CoInitializeEx() failed!"));
}
inline ~CPCoInitializeEx(void)
{ CoUninitialize();
}
};

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<META http-equiv=Content-Type content="text/html; =
charset=iso-8859-1">
<META content="MSHTML 6.00.6001.18148" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2><</FONT><A
href="mailto:vaclavpich@atlas.cz"><FONT face=Arial
size=2>vaclavpich@atlas.cz</FONT></A><FONT face=Arial size=2>> =
wrote in
message </FONT><A
href="news:a86624e5-ceef-4c5c-a369-21f67fb935e4@d31g2000hsg.googlegroup=
s.com"><FONT
face=Arial
size=2>news:a86624e5-ceef-4c5c-a369-21f67fb935e4@d31g2000hsg.googlegrou=
ps.com</FONT></A><FONT
face=Arial size=2>...</FONT></DIV>
<DIV><FONT face=Arial size=2>> CObject::CObject()<BR>> =
{<BR>>  //
1) if ( FAILED( LoadLibrary(...) )) throw exception1;<BR>> =
<BR>> //
2) if ( FAILED(CoInitialize( 0 ))  throw exception2;<BR>>
<BR>> // 3) if ( FAILED( CoCreateInstance(....))) throw
exception3;<BR>> }<BR>> <BR>> CObject::~CObject()<BR>>
{<BR>>  // 1) release COM interface<BR>> <BR>> // 2)
CoUninitialize();<BR>> <BR>>  // 2) FreeLibrary<BR>>
}<BR></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>you should put the separate objects =
(HANDLE
returned by LoadLibrary, CoInitialize()/CoUninitialize() and =
CoCreateInstance())
into separate classes and combine these classes into base-class or =
member-class
relationships.</FONT></DIV>
<DIV><FONT face=Arial size=2>Doing it this way you don't have to =
clean up
yourself anymore but rely on the code generation features of the =
compiler. And
you can reuse these classes next time you're calling these
functions.</FONT></DIV>
<DIV><FONT face=Arial size=2>And the caller of you'r code will get =
rich error
information.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>class
CPLoadLibrary<BR>{ private:<BR> HINSTANCE
h;<BR> public:<BR> inline CPLoadLibrary(const _TCHAR
*pName)<BR> { if (!(h =
LoadLibrary(pName)))<BR>   throwSystemException(<BR> =
     
GetLastError(),<BR>      
CString(_T("LoadLibrary(\"")) + CString(pName) +
CString(_T("\")")));<BR> }<BR> inline
~CPLoadLibrary(void)<BR> { FreeLibrary(h);<BR> }<BR> =
inline
void *getProcAddress(const char *pName)<BR> { void =
*p;</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>  if (!(p = =
::GetProcAddress(h,
pName)))<BR>   throwSystemException(<BR>   =
   
GetLastError(),<BR>      
_T("GetProcAddress()"));<BR>  return =
p;<BR> }<BR> inline
operator HINSTANCE (void)<BR> { return =
h;<BR> }<BR> inline
HINSTANCE getHINSTANCE(void)<BR> { return
h;<BR> }<BR>};</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>template<class T, const IID =
*_piREFIID>
<BR>class CPCoCreateInstance<BR>{ private:<BR> T
*m_p;<BR> public:<BR> inline
CPCoCreateInstance(<BR>     REFCLSID
_iCLSID,<BR>     IUnknown
*_pUnkOuter,<BR>     DWORD
_iClsContext)<BR> { HRESULT iRet;</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>  m_p = =
0;<BR>  if (FAILED(iRet
= CoCreateInstance(_iCLSID, _pUnkOuter, _iClsContext, *_piREFIID,
(void**)&m_p)))<BR>   throwSystemException(iRet,
_T("CoCreateInstance()"));<BR>  if
(!m_p)<BR>   throwSystemException(E_FAIL,
_T("CoCreateInstance()"));<BR> }<BR> inline
~CPCoCreateInstance(void)<BR> { if
(m_p)<BR>   m_p->Release();<BR> }<BR> inline =

operator T *(void)<BR> { return =
m_p;<BR> }<BR> inline T
*getPtr(void)<BR> { return m_p;<BR> }<BR> inline T
*detach(void)<BR> { T *pRet = m_p;<BR>  m_p =
0;<BR>  return pRet;<BR> }<BR>};<BR></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>class
CPCoInitializeEx<BR>{ private:<BR> public:<BR> inline
CPCoInitializeEx(void *_pReserved, DWORD =
_iFlags)<BR> { HRESULT
iRet;</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>  if (FAILED(iRet =
CoInitializeEx(_pReserved,
_iFlags)))<BR>   throwSystemException(iRet, =
_T("CoInitializeEx()
failed!"));<BR> }<BR> inline
~CPCoInitializeEx(void)<BR> { CoUninitialize();<BR> }<BR>}=
;</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
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