How do I use this member, declared in a header, as a function?

Question

These are some parts of my crawler header file. I cannot make changes to this header file.

private:
    int top_position;         // The maximum position of the throttle
    bool left_reverse;        // true if left direction is reverse
    bool right_reverse;       // true if right direction is reverse

So I tried to implement left_reverse in my implementation file. This is still a stub though.

bool left_reverse()
 {
   return(false);
 }

And I use it in implementing other function.

double Crawler::left_engine_speed() const
{
  double speedpercentage;
  double hundred(100.0);
  speedpercentage = left_throttle.flow()*hundred;
  if(left_reverse())     // <<< HERE IT IS 
    {
      speedpercentage=speedpercentage*(-1);
    }

  return(speedpercentage);
}

However I receive an error telling me error: '((const Vehicles::Crawler*)this)->Vehicles::Crawler::left_reverse' cannot be used as a function. Can someone tell me the problem here?

It's been a while since I wrote C++ instead of C, but doesn't that mean it's a `bool`, not a function returning a `bool`? — 2rs2ts, Feb 15 '14 at 01:06
@2rs2ts I am trying to use it as a bool function. But I dont know why I cannot. — user3312239, Feb 15 '14 at 01:20
I think it would be declared as `bool left_reverse();` if it was a function. — 2rs2ts, Feb 15 '14 at 01:21
I believe so too. But it is what I was given. I am only to implement it. :( — user3312239, Feb 15 '14 at 01:23
Do you think you were supposed to just make a class that uses that as a data member...? — 2rs2ts, Feb 15 '14 at 01:57

score 1 · Answer 1 · answered Feb 15 '14 at 03:58

1

It's not a function. It's a variable. There is no useful way to pretend it's a function. At all. Period.

answered Feb 15 '14 at 03:58

user253751

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Vlad from Moscow · Answer 2 · 2014-02-15T09:53:36.180

If the function is declared in some name space for example in the global name space then write

double Crawler::left_engine_speed() const
{
  double speedpercentage;
  double hundred(100.0);
  speedpercentage = left_throttle.flow()*hundred;
  if(::left_reverse())     // <<< HERE IT IS 
    {
      speedpercentage=speedpercentage*(-1);
    }

  return(speedpercentage);
}

or

if(SomeNameSpace::left_reverse())

Or

double Crawler::left_engine_speed() const
{
  bool left_reverse();
  double speedpercentage;
  double hundred(100.0);
  speedpercentage = left_throttle.flow()*hundred;
  if(left_reverse())     // <<< HERE IT IS 
    {
      speedpercentage=speedpercentage*(-1);
    }

  return(speedpercentage);
}

Here is a simple example

#include <iostream>

class Crawler
{
public:
    double left_engine_speed() const;
private:
    bool right_reverse; 
};

bool left_reverse() { return true; }

double Crawler::left_engine_speed() const
{
    if ( left_reverse() ) return 1.0;
    else return 0.0;
}

int main() 
{
    std::cout << Crawler().left_engine_speed() << std::endl;

    return 0;
}

Thanks for your help. But when I put the namespace in front of it, i receive an error saying it is not a member of the namespace. — user3312239, Feb 15 '14 at 01:22

How do I use this member, declared in a header, as a function?

2 Answers2