C++ Declaring An Array Of Function Pointers

Question

Basically I need to implement an event handler class, but run into an error that I cannot declare an array of voids:

class SomeClass
{
public:
    void registerEventHandler(int event, void (*handler)(std::string));

private:
    // here i get this error: declaration of ‘eventHandlers’ as array of void
    void (*eventHandlers)(std::string)[TOTAL_EVENTS];
}

void SomeClass::registerEventHandler(int event, void (*handler)(std::string))
{
    eventHandlers[event] = handler;
}



void handler1(std::string response)
{
    printf("ON_INIT_EVENT handler\n");
}
void handler2(std::string response)
{
    printf("ON_READY_EVENT handler\n");
}

void main()
{
    someClass.registerEventHandler(ON_INIT_EVENT, handler1);
    someClass.registerEventHandler(ON_READY_EVENT, handler2);
}

Can you help me figure out the exact syntax? Thanks!

SGrebenkin · Accepted Answer · 2015-02-05 10:20:41Z

11

This is not array of voids. It's array of function pointers. You should have defined it as follows:

void (*eventHandlers[TOTAL_EVENTS])(std::string);

Or better (C++14):

using event_handler = void(*)(std::string);
event_handler handlers[TOTAL_EVENTS];

Or C++03:

typedef void(*event_handler)(std::string);
event_handler handlers[TOTAL_EVENTS];

But I would rather recommend to do it using vector:

using event_handler = void(*)(std::string);
std::vector<event_handler> handlers;

edited Feb 5, 2015 at 10:20

answered Feb 5, 2015 at 10:12

SGrebenkin

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3 Comments

MSalters Over a year ago

Also, consider using event_handler = std::function<void(std::string)> - it will accept a larger number of callable objects, not just functions but also lambda expressions etc.

cubuspl42 Over a year ago

...and add a huge overhead

SGrebenkin Over a year ago

@cubuspl42 True. But not always. stackoverflow.com/questions/12452022/…

interjay · Accepted Answer · 2015-02-05 10:13:11Z

3

You are defining eventHandles as a pointer to a function returning an array of 5 voids, which is not what you intended.

Instead of trying to do this in one line, it will be easier and more readable by using a typedef:

typedef void (*event_handler_t)(std::string);
event_handler_t eventHandlers[TOTAL_EVENTS];

answered Feb 5, 2015 at 10:13

interjay

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Comments

harper · Accepted Answer · 2015-02-05 10:13:18Z

3

You mixed the event handler type and the array definition. Separate with typedef:

typedef void(*eventHandler)(std::string);
eventHandler eventHandlers[TOTAL_EVENTS];

answered Feb 5, 2015 at 10:13

harper

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