CODEWITHSUNDEEP
c++function-pointers
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Reputation: 391

Function pointer delclaration in c++

I have written a class Seat in cpp & I declared a function pointer it it. class implimentation is given below

Seat.cpp

#include "StdAfx.h"
#include "Seat.h"

int Seat::count = FL;
Seat::Seat(void)
{
   seatId = Seat::count;
   seatStatus = unoccupied;
   Seat::count++;
}

Seat::~Seat(void)
{

}


void Seat::*checkSeatStatus(void)
{


}

Seat.h

#include <string>
using namespace std;

 class Seat :
    public Vehicle
{
    int seatId;
    int seatStatus;
    static int count;

public:
   Seat(void);
   ~Seat(void);
   void (*checkSeatStatus)();
};

it showing error at function pointer declaration :

'checkSeatStatus' : illegal use of type 'void'

What is the reason behind ? , does it need any initialization of function pointer ?

Upvotes: 0

Views: 102

Answers (2)

Some programmer dude
Some programmer dude

Reputation: 409196

This doesn't answer the question you ask, but will show how to use the function in a thread.

Using std::thread it's actually very easy to start a thread using any member function. The important part is that it should be a normal member function, so declared like

class Seat
{
    ...
public:
    ...
    void checkSeatStatus();
};

Then to create a thread using the function you first need an instance of the class:

Seat seat;

And then you simply create the thread

std::thread my_thread{&Seat::checkSeatStatus, seat};

Do whatever other processing you want to do in the main thread, and then join the thread you had created:

my_thread.join();

There are a couple of important things to know here: The instance of the Seat class (the variable seat above) must live longer than the thread. If it goes out of scope and is destructed before the end of the thread that will lead to undefined behavior.

You must also join the tread before the thread-object (the variable my_thread above) is destructed.

Upvotes: 0

Alnitak
Alnitak

Reputation: 339816

If checkSeatStatus is intended to be a member function it should be:

void* Seat::checkSeatStatus(void) {
    ...
}

with function prototype within the class declaration of:

void* checkSeatStatus(void);

If it's intended to be a member variable holding a function pointer that you can set then, umm, don't do that... It's very probably the wrong design.

If (per the name) it's just supposed to return the current value of status then it should be a function that returns an int instead of a void *:

int Seat::checkStatus(void) {
    return status;
}

NB: I removed Seat from the method name since it should be implicit from the fact that you called it on a Seat object.

Upvotes: 2

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