You might use the union trick:
#include <iostream>
#include <sstream>
#include <iomanip>
using namespace std;
union ulf
{
unsigned long ul;
float f;
};
int main()
{
ulf u;
string str = "41BD9A69";
stringstream ss(str);
ss >> hex >> u.ul;
float f = u.f;
cout << f << endl;
}