Using #define to on and off functions

Projects Programming
1

Hello Friends,
I have created configuration.h file, where I want to run or don't run some functions in the sketch. For example
#define motor_direction 0 // if 0 clockwise, if 1 counterclockwise.
I can do this way:
if(motor_direction == 0)
clockwise();
if(motor_direction == 1)
counterclockwise();

But I believe it must be something like this
#if def motor_direction = 0
clockwise();
#endif

But how correctly?
Thanks!

2

if this is that simple and just a function call, you could do:

in your config.h file

// comment out the one you don't want
#define runMotor clockwise
//#define runMotor counterclockwise

in your code

#include "config.h"
...

  runMotor();

the text runMotor will be textually replaced by whatever you wrote in the .h by the preprocessor and so the right function will end up being called.

1 Like
3

https://en.cppreference.com/w/cpp/preprocessor

#if motor_direction == 0
clockwise();
#elif motor_direction == 1
anticlockwise();
#else
#error "Invalid motor_direction setting!"
#endif

Note that final else to catch an invalid definition of motor_direction

Note that this all happens at compile time - so you would have to rebuild and reload the sketch to change the motor direction.

Note that it's conventional to use ALL_UPPERCASE names for #defined symbols - so distinguish them from actual program variables.

4

an example

6

Thank you very much for fast replay!
One more question, how it works if;
#define sensor 2 // 1 - GPS, 2 - COMPASS, 3 - TEMPERATURE

void sensor_work()
{

analogRead(GPS);

analogRead(COMPASS);

analogRead(TEMPERATURE);

}

8

This is my personal opinion, but I consider #define/#ifdef to be a necessary evil to be avoided as much as possible.

In your case, I would make motor_direction a constant.

const int motor_direction = 1;
9

No. The compiler evaluates all constant conditions at compile time and omits all false branches. IMO this happens already at the lowest optimization level.

10

A better approach would be

enum INPUTS {GPS=1, COMPASS, TEMPERATURE};
...
analogRead(GPS);

analogRead(COMPASS);

analogRead(TEMPERATURE);

Normally the benefit of using an enumeration instead of a #define is that you get compiler checking of types and it reduces the errors you could make. In this case you don't get that because the parameter type to analogRead(x) is an int, but it makes for more readable code.

1 Like
11

So now in my configuration.h file I have:

sensor_type 2 // 1 - sensor A, 2 - sensor B, 3 - sensor C

in main file I have:

void sensors()
{
/// IF Sensor A run only this part

a = analogRead(A0);
output = map(a, 0, 100, 0, 10);

////END

/// IF Sensor B run only this part

b = analogRead(A1);
output = map(b, 0, 1000, 0, 10);

////END

/// IF Sensor C run only this part

c = analogRead(A0);
output = map(c, 0, 2000, 0, 10);

////END

}

what is the best way in my case?
Thank you all for leaving me an answer!

12

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2 Likes
13

And don't ask questions about code that clearly will not compile, please.

14

well that's his question - how to write that code with #ifdef or #if I suppose

but without code tags even for pseudo code, I'm out

15

Thanks guys! I get it!

#include "config.h"

void setup() {
  Serial.begin(115200); Serial.println();
}

void loop() {
  stop();
}

void STOPPWM() {Serial.println("SOFT STOP");}
void STOP() {Serial.println("NORMAL STOP");}

and here my define file:

// comment out the one you don't want
//#define stop STOPPWM
#define stop STOP

#if !defined(stop)
#error You need to pick one
#endif

Now the question is it correct way if I add more defines? For example:
#define turn_left SOFT_START
#define turn_left NORMAL_START

Should I just add in define.h like this?

//#define turn_left SOFT_START
#define turn_left NORMAL_START

#if !defined(turn_left)
#error You need to pick one
#endif

// comment out the one you don't want
//#define stop STOPPWM
#define stop STOP

#if !defined(stop)
#error You need to pick one
#endif

Thank you very much! This define option allows me to change things in my code very fast and easy! I am really very happy!

16

And one more question.. if I look at this code at first time, how do I know that void STOPPWM(); "belongs" to stop(); ?

#include "config.h"

void setup() {
  Serial.begin(115200); Serial.println();
}

void loop() {
  stop();
}

void STOPPWM() {Serial.println("SOFT STOP");}

void STOP() {Serial.println("NORMAL STOP");}
18

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