Class object initialization

Question

Hi I know this seems like a really dumb question and honestly I'm lost on what is causing this object error and could really use some help.

I have this class here :

class PriorityQueue {
  public:
    PriorityQueue(std::size_t max_nodes);
    void insert(Key k);
    void insert(KeyValuePair kv);
    KeyValuePair min();
    KeyValuePair removeMin();
    bool isEmpty() const;
    size_t size() const;
    nlohmann::json JSON() const;

  private:
    void heapifyUp(size_t i);
    void heapifyDown(size_t i);
    void removeNode(size_t i);
    Key getKey(size_t i);

    std::vector<KeyValuePair>   nodes_;
    size_t                      max_size_;
    size_t                      size_;

    const static size_t         ROOT = 1;
};  // class PriorityQueue

#endif  // _PRIORITYQUEUE_H_

Everything is properly defined in the corresponding cpp file for it. Now I'm trying to call it in a separate file that includes both as a header.

#include "priorityqueue.cpp"
#include "priorityqueue.h"

But in my main() function when I try to call the class to an object like

PriorityQueue m;

I get the error

no matching function for call to ‘PriorityQueue::PriorityQueue()’
PriorityQueue m;

I know this seems like a really basic C++ question but I have no idea what I am doing wrong. Any help would be greatly appreciated.

#include "priorityqueue.cpp" - This is only going to cause you grief down the line. Get out of the habit. It's better to work with the way C++ is compiled and linked. — StoryTeller - Unslander Monica
– StoryTeller - Unslander Monica, Commented Feb 25, 2019 at 6:49

mksteve · Accepted Answer · 2019-02-25 07:37:35Z

5

At the first, remove #include "priorityqueue.cpp" and just use of #include "priorityqueue.h"

Because your constructor has a parameter :

PriorityQueue(std::size_t max_nodes);

So, you should set max_nodes when you creating an object :

PriorityQueue m(10);

But you can also implement a default constructor with a default parameter :

In the header file

// In this approach you can use a default constructor
// Declaration
class PriorityQueue {
  public:
    PriorityQueue(std::size_t max_nodes = 10);
    ...
};

In the cpp file

// Implementation
PriorityQueue::PriorityQueue(std::size_t max_nodes)
{
    max_size_ = max_nodes;
 // initialize members
}

Then you can create instance like bellow :

PriorityQueue m;      // max_size_ will be set to default value (10)
PriorityQueue n(7);   // max_size_ will be set to 7

Try online

edited Feb 25, 2019 at 7:37

mksteve

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answered Feb 25, 2019 at 6:48

BattleTested_закалённый в бою

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4 Comments

user3712347 Over a year ago

Yep, now I realize it lol. This was extremely helpful, thank you!

Daniel Langr Over a year ago

To avoid redundancy, you can also set a default argument for max_nodes parameter as follows: PriorityQueue(std::size_t max_nodes = /* default */ ) .... Then, it will be a default constructor as well.

Daniel Langr Over a year ago

@MohammadrezaPanahi You didn't understand my comment. You still have 2 distinct constructors. My point was that both these constructors may be easily merged into one. BTW, it's better to initialize member variables in a constructor initializer list than in constructor's body.

StoryTeller - Unslander Monica Over a year ago

It's worth stressing however that the default argument better appear at the class declaration to be of any use.

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