Error: "invalid use of non-static member function" while calling a function from my own class-method

Question

I'm having a bad time trying to call a correctly-working expression (ultra[currentSensor].ping_timer(echoCheck)) from an own class method (myclass::run) instead of from void loop().

I'm getting the following compiler error: "invalid use of non-static member function".

If I call ultra[currentSensor].ping_timer(echoCheck) directly from void loop() it gives me no error, so I may be missing something.

Here's the (shortened) piece of code which is generating the error:

#include <NewPing.h>
#define ULTRA_NUM 3
#define MAX_DISTANCE 200
class myclass {
 public:
 void run();
 void echoCheck();
 unsigned int distance[ULTRA_NUM];
 uint8_t currentSensor = 0;
};
NewPing ultra[ULTRA_NUM] = {
 NewPing(4, 5, MAX_DISTANCE),
 NewPing(6, 7, MAX_DISTANCE),
 NewPing(8, 9, MAX_DISTANCE)
};
void myclass::run() {
// ....
 ultra[currentSensor].ping_timer(echoCheck); // Compiler error
 }
void myclass::echoCheck() {
 if (ultra[currentSensor].check_timer())
 distance[currentSensor] = ultra[currentSensor].ping_result
}

ping_timer() is defined as it follows:

void NewPing::ping_timer(void (*userFunc)(void), unsigned int max_cm_distance) {
 if (max_cm_distance > 0) set_max_distance(max_cm_distance);
 if (!ping_trigger()) return;
 timer_us(ECHO_TIMER_FREQ, userFunc);
}

I hope any of you can help me!

Thanks in advance,

Eduardo

---

Edit: What I am trying to do is to adapt this example (from NewPing Arduino Library) so that the sonar ping (sonar[currentSensor].ping_timer(echoCheck)) is done from a class method, and not from void loop().

• Nick Gammon: This might help. There is a discussion about calling a class function from an ISR.

Answer 1

The problem is that echo_check isn't void echo_check() but void echo_check(myclass *this) because it's a member function of a class.

You can make the whole thing static (along with run()) by:

class myclass {
 public:
 static void run();
 static void echo_check();
};
static void myclass::run() {
 .... 
}
void myclass::echo_check() {
 ....
}

And then you call:

myclass::run();

instead of instantiating an object.

• eduherminio: mm seems to solve the problem, but I'm getting now compiler errors wherever the class members are used (and also inside the class definition): "invalid use of member 'Ultrabot::_xxxxxxx' in static member function"
• Majenko: A static function can only call other static functions or global normal functions, or functions of other classes that are defined as static members.
• eduherminio: So now I have compiling functions which can't make what they are supposed to? :/
• Majenko: I don't know since you never bothered to show us your real code, only some tiny snippet.
• eduherminio: It's not about bothering to do it or not, it's about trying not to bother you with all my partially built code. I hope it's more clear now with the edit.

Answer 2

Solved:

I moved the event handler out of the class, and made it static void.

Then the code compiled properly

D