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I have been working on a program that is supposed to balance a robot. I want to have the motors driven in separate threads, but I keep getting these errors:

In file included from /usr/arm-linux-gnueabi/include/c++/6/thread:39:0,
                 from /src/include/includes.hpp:5,
                 from /src/src/main.cpp:1:
/usr/arm-linux-gnueabi/include/c++/6/functional: In instantiation of 'struct std::_Bind_simple<void (*(const char*, std::reference_wrapper<int>, std::reference_wrapper<bool>))(std::__cxx11::basic_string<char>, int*, bool*)>':
/usr/arm-linux-gnueabi/include/c++/6/thread:138:26:   required from 'std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (&)(std::__cxx11::basic_string<char>, int*, bool*); _Args = {const char (&)[15], std::reference_wrapper<int>, std::reference_wrapper<bool>}]'
/src/src/main.cpp:10:83:   required from here
/usr/arm-linux-gnueabi/include/c++/6/functional:1365:61: error: no type named 'type' in 'class std::result_of<void (*(const char*, std::reference_wrapper<int>, std::reference_wrapper<bool>))(std::__cxx11::basic_string<char>, int*, bool*)>'
       typedef typename result_of<_Callable(_Args...)>::type result_type;
                                                             ^~~~~~~~~~~
/usr/arm-linux-gnueabi/include/c++/6/functional:1386:9: error: no type named 'type' in 'class std::result_of<void (*(const char*, std::reference_wrapper<int>, std::reference_wrapper<bool>))(std::__cxx11::basic_string<char>, int*, bool*)>'
         _M_invoke(_Index_tuple<_Indices...>)
         ^~~~~~~~~
CMakeFiles/balance.dir/build.make:62: recipe for target 'CMakeFiles/balance.dir/src/main.cpp.o' failed
make[2]: *** [CMakeFiles/balance.dir/src/main.cpp.o] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/balance.dir/all' failed
make[1]: *** [CMakeFiles/balance.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2

My code looks like this:

main.cpp

#include "includes.hpp"

int main() {
    PID pid(1, 0, 0);

    int rightSpeed = 0;
    int leftSpeed = 0;
    bool end = false;

    std::thread m_right(motorThread, OUTPUT_A, std::ref(rightSpeed), std::ref(end));
    std::thread m_left(motorThread, OUTPUT_D, std::ref(leftSpeed), std::ref(end));

    gyro_sensor gyro(INPUT_2);
    gyro.set_mode(gyro_sensor::mode_gyro_ang);

    while(button::enter.pressed() == false) {
        rightSpeed, leftSpeed = pid.call(gyro.angle(false));
    }
    end = true;
    m_right.join();
    m_left.join();

    return 0;
}

motorThread.cpp

#include "includes.hpp"

void motorThread(address_type address, int * speedVar, bool * endVar) {
    motor m_motor(address);
    m_motor.run_direct();
    while(*endVar == false) {
        m_motor.set_duty_cycle_sp(*speedVar);
    }
}

includes.hpp

#pragma once

#include <iostream>
#include <string>
#include <thread>
#include <functional>

#include "ev3dev.h"
#include "pid.hpp"

using namespace ev3dev;

void motorThread(address_type address, int * speedVar, bool * endVar);

I am using the ev3dev docker image (page that tells you how to use it) with arm-linux-gnueabi-g++ 6.3.0 on Arch Linux.

Russell Hynes
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    `motorThread` takes pointers, not references, for the last two parameters – Mat Mar 24 '20 at 20:09
  • But don’t you pass references to pointers? – Russell Hynes Mar 24 '20 at 23:15
  • @RussellHynes No, though pointers can be looked at as some kind of reference, pointers (like `int *)` and references (like `int &`) are different things. See also [this question](https://stackoverflow.com/questions/57483/what-are-the-differences-between-a-pointer-variable-and-a-reference-variable-in?rq=1) – Lukas-T Mar 25 '20 at 07:47
  • So then how should I go about passing this pointer a memory address without references? – Russell Hynes Mar 25 '20 at 16:25

1 Answers1

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Used references instead of pointers in motorThread and it built.

Russell Hynes
  • 119
  • 6