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CComBSTRr  find replace

Posted on 2009-02-10
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Hi,

I've a CComBSTR variable as below:
CComBSTR bstrUrl= L"https://www.experts-exchange.com/";

Here, how to change the  "https" into "http"  in the above string. No MFC involved so CString cannot be used.

Thanks in advance


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Question by:mnopix
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Expert Comment

by:mrwad99
ID: 23610090
The underlying storage for a CComBSTR is the public member CComBSTR::m_str, which is a BSTR.  Now, a BSTR is typdef'ed as OLECHAR *BSTR, and an OLECHAR* is typdef'ed as a WCHAR.  A WCHAR is a wchar_t, so it follows then that all a CComBSTR is is a wrapper around a wchar_t*.

Internally, the constructor has the code

m_str = ::SysAllocString(pSrc);

where pSrc is the string you passed in.  The destructor, I would assume, calls SysFreeString, passing m_str.  (I cannot prove this since I cannot step into the destructor for some reason).  

Anyway, that being said, you can see that you can use standard wide string handling API functions to manipulate the member m_str, or, as I did, std::wstring, which is a lot easier.  The only thing you need to watch out for is that you take care of the memory occupied by m_str, if, for example, you increase the length of it.  You could write a wrapper function to do a replace operation, something like the code below.

HTH
      
void ReplaceInCComBSTR ( CComBSTR& strInput, const std::wstring& strOld, const std::wstring& strNew )
{
     std::wstring strOutput (  strInput );
     int pos = 0;
     int lpos = 0;
     while ( ( pos = strOutput.find ( strOld, lpos ) ) != string::npos )
     {
           strOutput.replace ( pos, strOld.length(), strNew );
           lpos = pos+1;
     }
 
	 // Find and replace is complete; now update the CComBSTR!
	 ::SysFreeString ( strInput.m_str );
	 strInput.m_str = ::SysAllocString ( strOutput.c_str() );
}
 
// ...
 
	CComBSTR bstrUrl=  L"https://www.experts-exchange.com/";
 
	ReplaceInCComBSTR ( bstrUrl, L"https:", L"http:" );

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Expert Comment

by:mrwad99
ID: 23610099
>> and an OLECHAR* is typdef'ed as a WCHAR

should be

and an OLECHAR is typdef'ed as a WCHAR (no pointer type)
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Author Comment

by:mnopix
ID: 23614713
I'm getting following compile errors:
abc.cpp(1716) : error C2653: 'string' : is not a class or namespace name
abc.cpp(1716) : errorC2065: 'npos' : undeclared identifier

Am I missing some include files?
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Author Comment

by:mnopix
ID: 23614748
About the Build Environment:
Windows Server 2003
Platform Builder for MS Windows CE 5.0
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Accepted Solution

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mrwad99 earned 500 total points
ID: 23620402
OK, you need to #include <string>
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Author Closing Comment

by:mnopix
ID: 31545385
Thank you very much for your effort. As our project approch was changed we decided keep the 'https' as its.  So I've not verified the last comment.
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LVL 19

Expert Comment

by:mrwad99
ID: 23631001
No problem, you will find it works :)
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