Перевод значения строки в вещественные переменные

#include <stdint.h>
 
#pragma pack(push, 1)
struct UtcOffs {
    double a0;     // Constant term of polynomial [s] 
    float a1;      // First order term of polynomial [s/s] 
    uint32_t tot;   // Reference time of week [s] 
    uint16_t wnt;   // Reference week number [] 
    uint8_t dtls;  // Delta time due to leap seconds [s] 
    uint8_t dn;     // 'Future' reference day number [1…7] [] 
    uint16_t wnlsf; // 'Future' reference week number [] 
    uint8_t dtlsf;  // 'Future' delta time due to leap seconds [s] 
};
 
struct GpsUtcParam { 
    UtcOffs utc; // GPS UTC time offset parameters 
    uint8_t cs;  // Checksum 
}; 
#pragma pack(pop)

int main()
{
    GpsUtcParam data;
    
    std::cout << sizeof(data);
}

#include <iostream>
#include <fstream>
 
int main()
{
    auto fname = "new.jps";
    std::ifstream f(fname, std::ifstream::binary);
 
    std::string s;
    while (f >> s) {
        if (s.substr(0, 2) == "UO") {
            double a0 = *reinterpret_cast<const double*>(s.substr(5, 8).data());
            float a1 = *reinterpret_cast<const float*>(s.substr(13, 4).data());
            std::cout << "a0: " << a0 << "; a1: " << a1 << std::endl;
        }
    }
    return 0;
}