_bstr_t 클래스 사용법

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_bstr_t Class

Microsoft Specific

A _bstr_t object encapsulates the BSTR data type. The class manages resource allocation and deallocation through function calls to SysAllocString and SysFreeString and other BSTR APIs when appropriate. The _bstr_t class uses reference counting to avoid excessive overhead.

Construction

_bstr_t

Constructs a _bstr_t object.

Operations

Assign	Copies a BSTR into the BSTR wrapped by a _bstr_t.
Attach	Links a _bstr_t wrapper to a BSTR.
copy	Constructs a copy of the encapsulated BSTR.
Detach	Returns the BSTR wrapped by a _bstr_t and detaches the BSTR from the _bstr_t.
GetAddress	Points to the BSTR wrapped by a _bstr_t.
GetBSTR	Points to the beginning of the BSTR wrapped by the _bstr_t.
length	Returns the number of characters in the _bstr_t.

Operators

operator =	Assigns a new value to an existing _bstr_t object.
operator +=	Appends characters to the end of the _bstr_t object.
operator +	Concatenates two strings.
operator !	Checks if the encapsulated BSTR is a NULL string.
operator ==, !=, <, >, <=, >=	Compares two _bstr_t objects.
operator wchar_t* | char*	Extract the pointers to the encapsulated Unicode or multibyte BSTR object.

// _bstr_t_Assign.cpp

#include <comdef.h>
#include <stdio.h>

int main()
{
    // creates a _bstr_t wrapper
    _bstr_t bstrWrapper;

    // creates BSTR and attaches to it
    bstrWrapper = "some text";
    wprintf_s(L"bstrWrapper = %s\n",
              static_cast<wchar_t*>(bstrWrapper));

    // bstrWrapper releases its BSTR
    BSTR bstr = bstrWrapper.Detach();
    wprintf_s(L"bstrWrapper = %s\n",
              static_cast<wchar_t*>(bstrWrapper));
    // "some text"
    wprintf_s(L"bstr = %s\n", bstr);

    bstrWrapper.Attach(SysAllocString(OLESTR("SysAllocedString")));
    wprintf_s(L"bstrWrapper = %s\n",
              static_cast<wchar_t*>(bstrWrapper));

    // assign a BSTR to our _bstr_t
    bstrWrapper.Assign(bstr);
    wprintf_s(L"bstrWrapper = %s\n",
              static_cast<wchar_t*>(bstrWrapper));

    // done with BSTR, do manual cleanup
    SysFreeString(bstr);

    // resuse bstr
    bstr= SysAllocString(OLESTR("Yet another string"));
    // two wrappers, one BSTR
    _bstr_t bstrWrapper2 = bstrWrapper;  

    *bstrWrapper.GetAddress() = bstr;

    // bstrWrapper and bstrWrapper2 do still point to BSTR
    bstr = 0;  
    wprintf_s(L"bstrWrapper = %s\n",
              static_cast<wchar_t*>(bstrWrapper));
    wprintf_s(L"bstrWrapper2 = %s\n",
              static_cast<wchar_t*>(bstrWrapper2));

    // new value into BSTR
    _snwprintf_s(bstrWrapper.GetBSTR(), 100, bstrWrapper.length(),
                 L"changing BSTR");  
    wprintf_s(L"bstrWrapper = %s\n",
              static_cast<wchar_t*>(bstrWrapper));
    wprintf_s(L"bstrWrapper2 = %s\n",
              static_cast<wchar_t*>(bstrWrapper2));
}

결과값

bstrWrapper = some text
bstrWrapper = (null)
bstr = some text
bstrWrapper = SysAllocedString
bstrWrapper = some text
bstrWrapper = Yet another string
bstrWrapper2 = some text
bstrWrapper = changing BSTR
bstrWrapper2 = some text

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