how to test if CComBSTR is empty

Question

How to test if a CComBSTR is an empty string? (with no 'text' value, can be "" or can be null)

my ideas:

test if CComBSTR::ByteLength() returns 0
test if CComBSTR::GetStreamSize() returns 0
test if CComBSTR::m_str is NULL
test if CComBSTR::Length() returns 0

which one is correct approach? if none of them is, then what is correct approach?

thanks.

score 2 · Accepted Answer · answered Jun 17 '11 at 09:42

2

4) Test length 0 it's fast as it's stored

answered Jun 17 '11 at 09:42

Tom

43,583
4
41
61

Actually it results in `SysStringLength()` being called which is not the fastest thing in the world. – sharptooth Jun 17 '11 at 11:22
2

Why's it slow? They're length prepended. – Tom Jul 14 '11 at 03:11

score 0 · Answer 2 · answered Oct 07 '14 at 11:42

3) test if CComBSTR::m_str is NULL

If you check the source code of CComBSTR there's several operators you can use to do this test:

bool CComBSTR::operator!() const throw()
bool CComBSTR::operator!=(int nNull) const throw()
bool CComBSTR::operator==(int nNull) const throw()
operator CComBSTR::BSTR() const throw()

For example:

CComBSTR value;
if (!value) { /* NULL */ } else { /* not NULL */ }
if (value != NULL) { /* not NULL */ } else { /* NULL */ }
if (value == NULL) { /* NULL */ } else { /* not NULL */ }
if ((BSTR) value) { /* not NULL */ } else { /* NULL */ }

how to test if CComBSTR is empty

2 Answers2