Convert Double to Char.

I need help in converting my x,y,z value from double to char.

1. Assume DUE which supports 64-bit binary64 (IEEE-754 Standard) format for floating point number. It gives 12/13 digit accuracy after decimal point.

2. Assume: double x = 3.1415926;

3. Execution of --

String storage = String(x, 7); results in having:

storage[0] = 0x33      //ASCII code of 3
storage[1] = 0x2E      //ASCII code of .
.....................................................
storage[8] = 0x36     //ASCII code 6
storage[9] = 0x00     //ASCII code of null-byte (null character)

4. Let us check:

Serial.println(storage); //shows: 3.1415926
Serial.println(storage[0], HEX); //shows: 33 = ASCII code of 3
..................................................
Serial.println(storage[9], HEX);  //shows: 0 = ASCII code of null character