Array constructor with function pointers?

Question

I'm trying to create a task list which should be used in task scheduler later in main loop(). I tried to use constructor but compiler throws an error could not covert '{doKeypad,2000,0}' from '<brace-enclosed initializer list>' to 'Task'

struct Task{
    void (*proc)();                     // Process callback
    unsigned long dly;                  // delay in ms
    unsigned long mls = 0;              // last run in millis()
};

Task task[] = {                         // This is much more readable 
    {doKeypad, 2000, 0},                // but it does not work :)
    {doPower,    10, 0},
    {doDallas,  800, 0},
    {doLcd,     500, 0}
};

void doKeypad(){
     // some code here... 
}
// rest of code follows - doPower(), doDallas() ...

What would be the simplest way of achieving this? I can do a function to fill the task array manually but it looks ugly and it is not very readable. I have seen some similar questions but they were about classes and too complicated for me :/

Also, it's purely a stylistic preference but when I want to initialize a function pointer, I use the address-of operator &functionname just like I would do if making a data pointer. The bare function name will decay to a pointer, but it's not as clear to a reader that you are dealing with a function pointer as opposed to a function object of some type. — Ben Voigt
– Ben Voigt, Commented Dec 30, 2016 at 23:33
On a C++ compiler, assuming correct prototypes, it compiles fine for me: rextester.com/RXVP25357 Perhaps your compiler doesn't support the C++ standard? — Ben Voigt
– Ben Voigt, Commented Dec 30, 2016 at 23:36
Guys, I'm new to C, I don't really know what is the difference between C and C++. This is Arduino 1.6.8 compiler. — Combinatix
– Combinatix, Commented Dec 30, 2016 at 23:43

Combinatix · Accepted Answer · 2016-12-31 00:57:54Z

1

Oh, I got it. The error is in the struct:

struct Task{
    void (*proc)();
    unsigned long dly;
    unsigned long mls = 0;  // < There should not be = 0
};

After removing it, it compiles fine.

edited Dec 31, 2016 at 0:57

answered Dec 30, 2016 at 23:58

Combinatix

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2 Comments

lakeweb Over a year ago

Ahh yes. And why the constructor mitigates the problem. One up.

Jarod42 Over a year ago

Aggregate property changes in this regards from C++11 to C++14. In C++11, that initialization in class avoid the class to be an aggregate. It is no longer true in C++14.

lakeweb · Accepted Answer · 2016-12-30 23:53:59Z

0

See if your compiler is looking for a constructor:

typedef void( *aproc ) ( );
struct Task{
    void (*proc)();                     // Process callback
    unsigned long dly;                  // delay in ms
    unsigned long mls = 0;              // last run in millis()
    Task( aproc a, unsigned long b, unsigned long c ) { proc= a; dly= b; mls= c; }
};

answered Dec 30, 2016 at 23:53

lakeweb

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