how to transform a double into an array of bytes in c

Question

I am writing a program in c that runs on 32-bit Microcontroller. I have a double and I want to transform it into an array of bytes. These bytes will be later sent to another microcontroller. But I do not know which method I should use to perform this task. Any Suggestion? The Problem consists in the inability in c to define a function that returns an array. So I must define an array outside the function and then process it inside the c-function which does not satisfy my needs

A function can return a struct or union.

Lee Daniel Crocker
– Lee Daniel Crocker

2015-08-06 19:23:58 +00:00
Commented Aug 6, 2015 at 19:23 — Lee Daniel Crocker
– Lee Daniel Crocker, Commented Aug 6, 2015 at 19:23

Kninnug · Accepted Answer · 2015-08-06 18:55:10Z

1

You can use type-punning through a union:

union{
    double d;
    unsigned char bytes[sizeof(double)];
} d2b;

d2b.d = 3.14;

You can access the bytes through d2b.bytes. Note that this assumes both micro-controllers use the same (internal) representation for doubles. If not, use some sort of serialization.

Edit:

Seeing your edit. You could also just memcpy and 'return' it through an output-parameter:

unsigned char * doubleToBytes(unsigned char bytes[sizeof(double)], double d){
    return memcpy(bytes, &d, sizeof d);
}

edited Aug 6, 2015 at 18:55

answered Aug 6, 2015 at 18:47

Kninnug

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