Return an array of bytes OR passing an array into a function

Question

What I am trying to accomplish is either return an array of bytes in a function so that I can do:

byte array[8] = function();

I am using my self made library to get values with the i2c bus. This is the library:

#ifndef MPULIBRARY_HPP
#define MPULIBRARY_HPP
#include "hwlib.hpp"

namespace mpulibrary{
class mpumanager
{
private:
    hwlib::i2c_bus_bit_banged_scl_sda bus;
    byte startregister[2] = {0x6B, 0};
    byte adress = 0x68;
    byte xregister[8] = {0x3B};
    byte yregister[8] = {0x3D};
    byte zregister[8] = {0x3F};
public:

    mpumanager(hwlib::i2c_bus_bit_banged_scl_sda bus):
        bus(bus)
    {}

    void startup(){
        bus.write(adress, startregister, 2);
    }   

    byte getXaxis(){
        bus.write(adress, xregister, 1);
        bus.read(adress, xregister, 2);
        return xregister[8];
    }
    byte getYaxis(){
        bus.write(adress, yregister, 1);
        bus.read(adress, yregister, 2);
        return yregister[8];
    }
    byte getZaxis(){
        bus.write(adress, zregister, 1);
        bus.read(adress, zregister, 2);
        return zregister[8];
    }

};
};
#endif // MPULIBRARY_HPP

My other code:

 auto manager = mpulibrary::mpumanager(i2c_bus);

 for(;;){
    manager.startup();

    byte ydata[8] = {};
    manager.getYaxis(ydata[8]);


    byte zdata[8] = {0x3F};
    i2c_bus.write(adress, zdata, 1);
    i2c_bus.read(adress, zdata, 2);

    int16_t yaxis = 0;
    int16_t zaxis = 0;
    yaxis = (ydata[0] << 8) + ydata[1];
    zaxis = (zdata[0] << 8) + zdata[1];

    hwlib::cout << "Y: " << yaxis << " Z:" << zaxis << "\n";
    hwlib::wait_ms(100);

 }

I hope someone can provide me an answer. Thanks in advance!

Jarod42 · Accepted Answer · 2016-06-14 11:47:44Z

2

byte array[8] = function();

You cannot directly with C-array.
You have to wrap it in a class (as std::array<byte, 8>).

byte xregister[8] = {0x3B};
byte getXaxis(){
    bus.write(adress, xregister, 1);
    bus.read(adress, xregister, 2);
    return xregister[8];
}

You may return reference to array:

byte xregister[8] = {0x3B};
using byte_array = byte[8]; // typedef to avoid strange syntax in return type

byte_array& getXaxis(){
    bus.write(adress, xregister, 1);
    bus.read(adress, xregister, 2);
    return xregister;
}

and use it:

auto& xAxis = manager.getXaxis();

edited Jun 14, 2016 at 11:47

answered Jun 14, 2016 at 11:41

Jarod42

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Comments

Dimitrios Bouzas · Accepted Answer · 2016-06-14 11:48:23Z

1

You could pass an array by reference if you could transform your function as:

template<int N>
void function(byte (&array)[N]) {

}

Or if you want to restrict the size as (e.g., 8):

void function(byte (&array)[8]) {

}

You can't return a raw array because C-style raw arrays are not copy-able.

answered Jun 14, 2016 at 11:48

Dimitrios Bouzas

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