Problem in allocating an array of objects with no default constructor

[yatko]

Hi,

I want to allocate an array of interprocess_semaphore object
initialized with 0 counter value. This class is a part of boost
library used for thread synchronization.

class interprocess_semaphore {
public:
// construct/copy/destruct
interprocess_semaphore(int);
~interprocess_semaphore();

// public member functions
void post() ;
void wait() ;
bool try_wait() ;
bool timed_wait(const boost:osix_time:time &) ;
};

---

interprocess_semaphore* ready_sem;

ready_sem = new interprocess_semaphore[maxFloor;

Since the class has no default constructor, the compiler gives error.
When I try to use vector, I solve the initialization problem. But at
this time, there is another roblem related with copying semaphores.

vector<interprocess_semaphore> ready_sem;

ready_sem.reserve(maxFloor);

for (int i = 0;i < maxFloor; ++i)
ready_sem.push_back(* new boost::interprocess::interprocess_semaphore
(0));

All I want to do is allocating an array of semephore objects with 0
initial counter value. How can I do that in C++ ?

yatko

 

[alfps]

vector<interprocess_semaphore> ready_sem;

ready_sem.reserve(maxFloor);

for (int i = 0;i < maxFloor; ++i)
        ready_sem.push_back(* new boost::interprocess::interprocess_semaphore
(0));

All I want to do is allocating an array of semephore objects with 0
initial counter value. How can I do that in C++ ?

Assuming the objects are copyable (copy constructor and assignment
operator),

vector<interprocess_semaphore> ready_sem( maxFloor, 0 );

Cheers & hth.,

- Alf

 

[amrollahi.saeed]

Hi,

I want to allocate an array of interprocess_semaphore object
initialized with 0 counter value. This class is a part of boost
library used for thread synchronization.

class interprocess_semaphore {
public:
  // construct/copy/destruct
  interprocess_semaphore(int);
  ~interprocess_semaphore();

  // public member functions
  void post() ;
  void wait() ;
  bool try_wait() ;
  bool timed_wait(const boost:osix_time:time &) ;

};

---

interprocess_semaphore* ready_sem;

ready_sem = new interprocess_semaphore[maxFloor;

Since the class has no default constructor, the compiler gives error.
When I try to use vector, I solve the initialization problem. But at
this time, there is another roblem related with copying semaphores.

vector<interprocess_semaphore> ready_sem;

ready_sem.reserve(maxFloor);

for (int i = 0;i < maxFloor; ++i)
        ready_sem.push_back(* new boost::interprocess::interprocess_semaphore
(0));

All I want to do is allocating an array of semephore objects with 0
initial counter value. How can I do that in C++ ?

yatko

Hi Yatko
I have the following suggestions for you:
1. If semaphore objects usually have initial value (0), it is better
to declare your class
like this:
class interprocess_semaphore {
public:
interprocess_semaphore(int = 0); // default ctor
// as before
};
2. Of course it is not a good idea, but if you like to use array over
vector, you can use the following code:
interprocess_semaphore** ready_sem = new interprocess_semaphore*
[maxFloor];

for (int i = 0; i < maxFloor; i++) {
interprocess_semaphore* p = new interprocess_semaphore(0);
ready_sem = p;
}

// use array ...

for (int i = 0; i < maxFloor; i++) {
delete ready_sem;
}

delete [] ready_sem;

Regards,
- Saeed

 

[yatko]

Hi all,

Thanks for your postings and I am very sorry that less information.

Hi Yatko
I have the following suggestions for you:
1. If semaphoreobjectsusually have initial value (0), it is better
to declare your class
like this:
  class interprocess_semaphore {
  public:
     interprocess_semaphore(int = 0); // default ctor
     // as before
  };

First, the interprocess_class is a part of boost library and it is
designed with one-parameter constructor. I could not have the chance
of redeclare the overall class.

2. Of course it is not a good idea, but if you like to usearrayover
vector, you can use the following code:
        interprocess_semaphore** ready_sem = new interprocess_semaphore*
[maxFloor];

        for (int i = 0; i < maxFloor; i++) {
                interprocess_semaphore* p = new interprocess_semaphore(0);
                ready_sem = p;
        }

        // usearray...

        for (int i = 0; i < maxFloor; i++) {
                delete ready_sem;
        }

        delete [] ready_sem;

Regards,
  - Saeed

Second, I have tried to use vector, but since the class is designed as
noncopyable, the compiler gives errors. Finally, I have decided to use
array of pointers and it works fine.

Thanks