In MFC program, you’d better try to avoid using std::string. There is no compelling reason to use it in MFC, and it leads to confusion.
There are some standard method to translate among Cstring ,string and char[].

// Suppose
CString str;
std::string s;
char buf[SIZE];
// from CString to std::string
s = str;
// from std::string to CString
str = s.c_str();
// to char[]
_tcscpy(buf, [...]