How can I convert ASCII string to BSTR using ATL framework and Win32 APIs?
ASCII strings are used in client and servers. However wide character strings are recomended to support verious local languages. DCOM parameters of strings are always BSTRs. So there is always a need to convert ASCII to wide char and then wide char to BSTRs. ATL framework has a set of helper macros to convert between these type of strings.
Mecro notations
Notation | Description |
A | ANSI character string. |
W | Unicode character string. |
T | Generic character string (equivalent to W when _UNICODE is defined, equivalent to A otherwise). |
OLE | OLE character string (equivalent to W). |
Mecro names
A2BSTR | OLE2A | T2A | W2A |
A2COLE | OLE2BSTR | T2BSTR | W2BSTR |
A2CT | OLE2CA | T2CA (Deprecated. Use T2CA_EX or CT2CA instead.) | W2CA |
A2CW | OLE2CT | T2COLE | W2COLE |
A2OLE | OLE2CW | T2CW | W2CT |
A2T | OLE2T | T2OLE | W2OLE |
A2W | OLE2W | T2W | W2T |
ComBSTR class
ComBSTR is one helper class provided by MFC/ATL to convert UNICODE string to BSTR and vice versa. It has verious public methods and operators for managing and manipulating BSTRs in COM servers and client.
ComBSTR methods
| Name | Description |
|---|---|
| CComBSTR::Append | Appends a string to m_str. |
| CComBSTR::AppendBSTR | Appends a BSTR to m_str. |
| CComBSTR::AppendBytes | Appends a specified number of bytes to m_str. |
| CComBSTR::ArrayToBSTR | Creates a BSTR from the first character of each element in the safearray and attaches it to the CComBSTR object. |
| CComBSTR::AssignBSTR | Assigns a BSTR to m_str. |
| CComBSTR::Attach | Attaches a BSTR to the CComBSTR object. |
| CComBSTR::BSTRToArray | Creates a zero-based one-dimensional safearray, where each element of the array is a character from the CComBSTR object. |
| CComBSTR::ByteLength | Returns the length of m_str in bytes. |
| CComBSTR::Copy | Returns a copy of m_str. |
| CComBSTR::CopyTo | Returns a copy of m_str via an [out] parameter |
| CComBSTR::Detach | Detaches m_str from the CComBSTR object. |
| CComBSTR::Empty | Frees m_str. |
| CComBSTR::Length | Returns the length of m_str. |
| CComBSTR::LoadString | Loads a string resource. |
| CComBSTR::ReadFromStream | Loads a BSTR object from a stream. |
| CComBSTR::ToLower | Converts the string to lowercase. |
| CComBSTR::ToUpper | Converts the string to uppercase. |
| CComBSTR::WriteToStream | Saves m_str to a stream. |
ComBSTR operators
| Name | Description |
|---|---|
| CComBSTR::operator BSTR | Casts a CComBSTR object to a BSTR. |
| CComBSTR::operator ! | Returns true or false, depending on whether m_stris NULL. |
| CComBSTR::operator != | Compares a CComBSTR with a string. |
| CComBSTR::operator & | Returns the address of m_str. |
| CComBSTR::operator += | Appends a CComBSTR to the object. |
| CComBSTR::operator < | Compares a CComBSTR with a string. |
| CComBSTR::operator = | Assigns a value to m_str. |
| CComBSTR::operator == | Compares a CComBSTR with a string. |
| CComBSTR::operator > | Compares a CComBSTR with a string. |
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