Arduino: struct pointer as function parameter

Question

The code below gives the error:

sketch_jul05a:2: error: variable or field 'func' declared void

So my question is: how can I pass a pointer to a struct as a function parameter?

Code:

typedef struct
{ int a,b;
} Struc;


void func(Struc *p) {  }

void setup() {
  Struc s;
  func(&s);
}

void loop()
{
}

Answer 1

The problem is, that the Arduino-IDE auto-translates this into C like this:

#line 1 "sketch_jul05a.ino"
#include "Arduino.h"
void func(Struc *p);
void setup();
void loop();
#line 1
typedef struct
{ int a,b;
} Struc;


void func(Struc *p) {  }

void setup() {
  Struc s;
  func(&s);
}

void loop()
{
}

Which means Struc is used in the declaration of func before Struc is known to the C compiler.

Solution: Move the definition of Struc into another header file and include this.

Main sketch:

#include "datastructures.h"

void func(Struc *p) {  }

void setup() {
  Struc s;
  func(&s);
}

void loop()
{
}

and datastructures.h:

struct Struc
{ int a,b;
};

Answer 2

The answer above works. In the meantime I had found the following also to work, without the need for a .h file:

typedef struct MyStruc
{ int a,b;
} Struc;

void func(struct MyStruc *p) {  }

void setup() {
  Struc s;
  func(&s);
}

void loop()
{
}

Be warned: Arduino coding is a little flaky. Many of the libraries are also a bit flaky!

Answer 3

This next code works for me as in Arduino 1.6.3:

typedef struct S
{
    int a;
}S;

void f(S * s, int v);



void f(S * s, int v)
{
    s->a = v;
}

void setup() {
}

void loop() {
    S anObject;
    // I hate global variables

    pinMode(13, OUTPUT);
    // I hate the "setup()" function

    f(&anObject, 0);
    // I love ADTs

    while (1) // I hate the "loop" mechanism
    {
        // do something
    }
}

Answer 4

Prolly old news, but typedef struct allows member functions (at least in IDE 1.6.4). Depending on what you want to do, of course, but I can't think of any func(struct *p) that couldn't be handled also with object.func(param pdata). Just that something like p->a = 120; becomes something like object.setA(120);

typedef struct {
   byte var1;
   byte var2;

   void setVar1(byte val){
      this->var1=val; 
   }

   byte getVar1(void) {
       return this->var1; 
   }
} wtf;

wtf testW = {127,15};

void initwtf(byte setVal) {
    testW.setVar1(setVal); 
    Serial.print("Here is an objective returned value: ");
    Serial.println(testW.getVar1());
} 
...
void loop() {
   initwtf(random(0,100));
}