How to convert IStream to Base64 string in c++ - c++

Question

I have IStream and I want to convert it to base 64 string in c++ so that I can use it in C++/cli to convert it to .net stream.
Similar way, I want to know how to convert base 64 string back to IStream.

Answer 1

My code uses ATL CString...
template<class T>
HRESULT StreamToBase64(IStream* pStream, T &strOut)
{
// Clear buffer
strOut.ReleaseBuffer(0);
if (!pStream)
return S_OK;
// Get size
STATSTG stat;
pStream->Stat(&stat, STATFLAG_NONAME);
unsigned iLen = stat.cbSize.LowPart;
// Seek to start
LARGE_INTEGER lPos;
lPos.QuadPart = 0;
HRESULT hr = pStream->Seek(lPos, SEEK_SET, nullptr);
if (FAILED(hr))
return hr;
// Reserve the memory
strOut.GetBuffer(Mfx::BinToBase64GetRequiredLength(iLen));
strOut.ReleaseBuffer(0);
// Use one line to decode a time. On line of Base64 code has usually 39 chars. We
// use a nearly 1kb buffer
const int iBase64LIneLen = 76/4*3;
BYTE bLine[(1024/iBase64LIneLen)*iBase64LIneLen];
ULONG bRead;
while (SUCCEEDED(hr = pStream->Read(bLine, sizeof(bLine), &bRead)) && bRead!=0)
strOut += T(Mfx::BinToBase64A(bLine, bRead));
// And seek back to start
pStream->Seek(lPos, SEEK_SET, nullptr);
return SUCCEEDED(hr) ? S_OK : hr;
}
HRESULT StreamToBase64(IStream* pStream, CStringA &strOut)
{
return StreamToBase64<CStringA>(pStream, strOut);
}
HRESULT StreamToBase64(IStream* pStream, CStringW &strOut)
{
return StreamToBase64<CStringW>(pStream, strOut);
}