Convert between double and byte array, for transfer over ZigBee API?

问题

I'm trying to take two doubles (GPS coordinates) and send them over the ZigBee API to another ZigBee receiver unit, but I don't know how to decompose the doubles into byte arrays and then re-compose them back into their original form once they are transferred.

Basically, I need to turn each double into an array of eight raw bytes, then take that raw data and reconstruct the double again.

Any ideas?

回答1:

What you're doing is called type punning.

Use a union:

union {
  double d[2];
  char b[sizeof(double) * 2];
};

Or use reinterpret_cast:

char* b = reinterpret_cast<char*>(d);

回答2:

Here's a rather unsafe way to do it:

double d = 0.123;
char *byteArray = (char*)&d;

// we now have our 8 bytes

double final = *((double*)byteArray);
std::cout << final; // or whatever

Or you could use a reinterpret_cast:

double d = 0.123;
char* byteArray = reinterpret_cast<char*>(&d);

// we now have our 8 bytes

double final = *reinterpret_cast<double*>(byteArray);
std::cout << final; // or whatever

回答3:

Typically a double is already eight bytes. Please verify this on your operating system by comparing sizeof(double) and sizeof(char). C++ doesn't declare a byte , usually it means char

If it is indeed true.

   double x[2] = { 1.0 , 2.0};

   double* pToDouble = &x[0];
   char* bytes = reinterpret_cast<char*>(pToDouble);

Now bytes is what you need to send to ZigBee

来源：https://stackoverflow.com/questions/8059775/convert-between-double-and-byte-array-for-transfer-over-zigbee-api