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_bstr_t::Assign

Microsoft Specific

Copies a BSTR into the BSTR wrapped by a _bstr_t.


void Assign(
   BSTR s
);

Parameters

s

A BSTR to be copied into the BSTR wrapped by a _bstr_t.

Assign does a binary copy, which means the entire length of the BSTR is copied, regardless of content.

// _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));
}

Output

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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