Splitting DOUBLE in byte for save on EEPROM

Question

I'm trying to save in memory (FRAM in this case) DOUBLE value, i try the same method with use of UNION for save FLOAT value, but don't go over the 2nd number after dot, why? Where I'm wrong? thank's for help .

 //---------------------------------------------------------
 union Scomp_double // si utilizza union x double
 {
 double temp;
 char byte_s[8];
 } S_double;
 //---------------------------------------------------------
double mioDouble = 1234567.12345678;
//-------------------------DOUBLE--------------------------------
 Serial.println("DOUBLE");
 byte d0 = 0; // contengono i byte del float
 byte d1 = 0;
 byte d2 = 0;
 byte d3 = 0;
 byte d4 = 0;
 byte d5 = 0;
 byte d6 = 0;
 byte d7 = 0;
 S_double.temp = mioDouble;
 d0 = S_double.byte_s[0];
 d1 = S_double.byte_s[1];
 d2 = S_double.byte_s[2];
 d3 = S_double.byte_s[3];
 d4 = S_double.byte_s[4];
 d5 = S_double.byte_s[5];
 d6 = S_double.byte_s[6];
 d7 = S_double.byte_s[7];
 Serial.println(d0);
 Serial.println(d1);
 Serial.println(d2);
 Serial.println(d3);
 Serial.println(d4);
 Serial.println(d5);
 Serial.println(d6);
 Serial.println(d7);
 fram.writeEnable(true);
 fram.write8(11, d0);
 fram.writeEnable(false);
 fram.writeEnable(true);
 fram.write8(12, d1);
 fram.writeEnable(false);
 fram.writeEnable(true);
 fram.write8(13, d2);
 fram.writeEnable(false);
 fram.writeEnable(true);
 fram.write8(14, d3);
 fram.writeEnable(false);
 fram.writeEnable(true);
 fram.write8(15, d4);
 fram.writeEnable(false);
 fram.writeEnable(true);
 fram.write8(16, d5);
 fram.writeEnable(false);
 fram.writeEnable(true);
 fram.write8(17, d6);
 fram.writeEnable(false);
 fram.writeEnable(true);
 fram.write8(18, d7);
 fram.writeEnable(false);
 S_double.byte_s[0] = fram.read8(11); // si ricompone il double
 S_double.byte_s[1] = fram.read8(12);
 S_double.byte_s[2] = fram.read8(13);
 S_double.byte_s[3] = fram.read8(14);
 S_double.byte_s[4] = fram.read8(15);
 S_double.byte_s[5] = fram.read8(16);
 S_double.byte_s[6] = fram.read8(17);
 S_double.byte_s[7] = fram.read8(18);
 double masterDouble = S_double.temp;
 Serial.println(masterDouble);
 //-------------------------DOUBLE-------------------------------

expected result 1234567.12345678 , result taken 1234567,12

• gre_gor: double on Arduino is 4 bytes. The same as a float.
• Francesco Valla: no way for have 4 digit after dot ,nice :) tnks for reply
• Mikael Patel: Why not simple use "fram.write(&aFloatVar, sizeof(aFloatVar));"??
• Francesco Valla: and what for read? tnks

Answer 1

how suggest in the comments, and on Arduino reference DOUBLE website

only on arduino 2 float it's 8 byte.

• Chris Stratton: If you mean on the Due, yes, but readers who don't speak Italian will not automatically map the actual name of the product "Arduino Due" to "Arduino 2" and understand that you are talking about an ARM-based board rather than a traditional AVR-based one where float and double are 4-byte types.

Answer 2

The problem here is the serial output, which by default only outputs 2 decimal places. Solution: Serial.println(masterDouble,8);