This function retrieves the length (in bytes) of a string.
The returned value can be different from fstrlen(bstr) if the following occurred:
If BSTR was allocated with SysAllocStringLen, SysReAllocStringLen or SysAllocStringByteLen
If the passed-in characters included a null character in the first len characters
For a BSTR allocated with SysAllocStringLen, SysReAllocStringLen, or SysAllocStringByteLen, this function always retrieves the number of bytes specified in the len parameter at allocation time.
Passing invalid (and under some circumstances NULL) pointers to this function causes an unexpected termination of the application.