How to use function name as parameter?

Question

I tried to pass function name as parameter as below:

class RemoteControlMonitor {
private:
    void (*rph)(unsigned int key);
    void (*rrh)(unsigned int key);

public:
    RemoteControlMonitor(void (*pressed)(unsigned int key), 
                     void (*released)(unsigned int key) = 0) {
     *rph = pressed;
     *rrh = released;
     lr_set_handler(remote_control_handler);
    }

    void runPressed() {
     while (!shutdown_requested()) {
         remote_key = 0;
         remote_etype = 0;
         wait_event(&remote_control_pressed, 0);

             if (*rph) {
                 (*rph)(remote_key);
             }
         }
     }
 };

when I compile it, the error is as below, what can I do?

RemoteControlMonitor.H: In method `RemoteControlMonitor::RemoteControlMonitor(void ()(unsigned int), void ()(unsigned int) = 0)':

RemoteControlMonitor.H:61: assignment of read-only location

RemoteControlMonitor.H:61: assignment to void ()(unsigned int)' fromvoid (*)(unsigned int)'

RemoteControlMonitor.H:62: assignment of read-only location

RemoteControlMonitor.H:62: assignment to void ()(unsigned int)' fromvoid (*)(unsigned int)'

*rph = pressed => rph = pressed (lose the star).

n. m. could be an AI
– n. m. could be an AI

2013-10-28 11:56:06 +00:00
Commented Oct 28, 2013 at 11:56 — n. m. could be an AI
– n. m. could be an AI, Commented Oct 28, 2013 at 11:56

SHR · Accepted Answer · 2013-10-28 12:35:01Z

2

try to use typedef it will be more clear.

typedef  void (*keyaction)(unsigned int key);

class RemoteControlMonitor {
private:
    keyaction rph;
    keyaction rrh;

public:
    RemoteControlMonitor(keyaction pressed, 
                     keyaction released = NULL) {
     rph = pressed;
     rrh = released;
     lr_set_handler(remote_control_handler);
    }

    void runPressed() {
     while (!shutdown_requested()) {
         remote_key = 0;
         remote_etype = 0;
         wait_event(&remote_control_pressed, 0);

             if (rph) {
                 (*rph)(remote_key);
             }
         }
     }
 };

EDIT:

this function goes to constructor:

void f(unsigned int){}

you declare it like this:

RemoteControlMonitor  rcm(f);

edited Oct 28, 2013 at 12:35

answered Oct 28, 2013 at 11:57

SHR

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4 Comments

mikezang Over a year ago

RemoteControlMonitor.H:58: invalid type void *' for default argument to void (*)(unsigned int)'

mikezang Over a year ago

Then I call it with function void my_remote_pressed(unsigned int key) {….} by rcm = new RemoteControlMonitor(&my_remote_pressed); compile error is In function int main(int, char **)': ANSI C++ forbids implicit conversion from void *' in default argument

mikezang Over a year ago

Follow your code, I did it as below: void my_remote_pressed(unsigned int key) { … } RemoteControlMonitor rcm(my_remote_pressed); int runRCM(int argc, char *argv) { rcm.runPressed(); return 0; } int main(int argc, char **argv) { execi(&runRCM, 0, 0, PRIO_NORMAL + 1, DEFAULT_STACK_SIZE); return 0; } The error is RemoteControlMonitor.H:58: invalid type void *' for default argument to void ()(unsigned int)' rcx1.C: In function void __static_initialization_and_destruction_0(int, int)': rcx1.C:54: ANSI C++ forbids implicit conversion from void *' in default argument What can I do next?

SHR Over a year ago

which line is 58? I guess you you can try to cast the NULL. (keyaction)NULL

GMasucci · Accepted Answer · 2013-10-28 12:02:08Z

2

you do not need to dereference you pointer, *rph, just call it as normal as rph and it should work fine, other wise you are trying to set the pointer *rph to pressed and not its value.

The *rph = pressed means set my memory location to pressed, where rph = pressed means set my value to pressed.

This link has some handy information in regards to references, pointers and dereferencing.

Hope this helps:)

answered Oct 28, 2013 at 12:02

GMasucci

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