Question

How to do the transform bstr_t to double in c++?

I was thinking to convert to *char, then *char to double?

Answer 1

If you have a char* or wchar_t* string, use the strtod/wcstod functions to read a double.

E.g. using @Steve’s suggestion:

_bstr_t x;
double q = wcstod(x, NULL); // implicit conversion!
double p = strtod(x, NULL); // same

Apparently _bstr_t has implicit conversion operators both to const char * and const wchar_t*, so you can use them directly in the float parsing functions.