No, just no. And, never use sscanf().

This is totally pointless when serialization to and from an unsigned integer that's binary equivalent would be perfectly reversible and therefore wouldn't lose any information.

    double f = 0.0/0.0; // might need some compiler flags to make this a soft error.
    double g;
    char s[9];

    assert(sizeof double == sizeof uint64_t);

    snprintf(s, 9, "%0" PRIu64, *(uint64_t *)(&f));

    snscanf(s, 9, "%0" SCNu64, (uint64_t *)(&g));

If you want something shorter, apply some sort of heuristic that doesn't sacrifice faithful reproduction of the original representation, e.g., idempotency.