C ++ 11 std :: vector模板类的构造函数中带有参数

Question

Hello all c++ experts,

I have a class template for a Circular buffer

#ifndef CIRCULAR_BUFFER_H
#define CIRCULAR_BUFFER_H

#include <algorithm>
#include <cstddef>
#include <cassert>
#include <stdexcept>
#include <iostream>

template <typename T>
class CircularBuffer
{
public:
    typedef size_t size_type;
    typedef T& reference;
    typedef const T& const_reference;
    typedef T* pointer;
    typedef const T* const_pointer;

    explicit CircularBuffer(size_type capacity);
    CircularBuffer(const CircularBuffer<T> &rhs);
    CircularBuffer(CircularBuffer<T>&& rhs);
    ~CircularBuffer() { if (_buffer) delete[] _buffer; }

    CircularBuffer<T>& operator=(CircularBuffer<T> rhs);

    size_type size() const { return (_full ? _capacity : _front); }
    size_type capacity() const { return _capacity; }
    bool is_full() const { return _full; }

    const_reference operator[](size_type index) const;
    reference operator[](size_type index);

    void add(T item);
    void resize(size_type new_capacity);

    friend void swap(CircularBuffer<T> &a, CircularBuffer<T> &b)
    {
        std::swap(a._buffer, b._buffer);
        std::swap(a._capacity, b._capacity);
        std::swap(a._front, b._front);
        std::swap(a._full, b._full);
    }

private:
    pointer _buffer;
    size_type _capacity;
    size_type _front;
    bool _full;

    CircularBuffer();
};

template<typename T>
CircularBuffer<T>::CircularBuffer()
    : _buffer(nullptr)
    , _capacity(0)
    , _front(0)
    , _full(false)
{
}

template<typename T>
CircularBuffer<T>::CircularBuffer(size_type capacity)
    : CircularBuffer()
{
    if (capacity < 1) throw std::length_error("Invalid capacity");

    _buffer = new T[capacity];
    _capacity = capacity;
}

template<typename T>
CircularBuffer<T>::CircularBuffer(const CircularBuffer<T> &rhs)
    : _buffer(new T[rhs._capacity])
    , _capacity(rhs._capacity)
    , _front(rhs._front)
    , _full(rhs._full)
{
    std::copy(rhs._buffer, rhs._buffer + _capacity, _buffer);
}

template<typename T>
CircularBuffer<T>::CircularBuffer(CircularBuffer<T>&& rhs)
    : CircularBuffer()
{
    swap(*this, rhs);
}

template<typename T>
typename CircularBuffer<T>::const_reference
CircularBuffer<T>::operator[](size_type index) const
{
    static const std::out_of_range ex("index out of range");
    if (index < 0) throw ex;

    if (_full)
    {
        if (index >= _capacity) throw ex;
        return _buffer[(_front + index) % _capacity];
    }
    else
    {
        if (index >= _front) throw ex;
        return _buffer[index];
    }
}

template<typename T>
typename CircularBuffer<T>::reference
CircularBuffer<T>::operator[](size_type index)
{
    return const_cast<reference>(static_cast<const CircularBuffer<T>&>(*this)[index]);
}

template<typename T>
CircularBuffer<T>&
CircularBuffer<T>::operator=(CircularBuffer<T> rhs)
{
    swap(*this, rhs);
    return *this;
}

template<typename T>
void
CircularBuffer<T>::add(T item)
{
    _buffer[_front++] = item;
    if (_front == _capacity) {
        _front = 0;
        _full = true;
    }
}

template<typename T>
void
CircularBuffer<T>::resize(size_type new_capacity)
{
    if (new_capacity < 1) throw std::length_error("Invalid capacity");
    if (new_capacity == _capacity) return;

    size_type num_items = size();
    size_type offset = 0;
    if (num_items > new_capacity)
    {
        offset = num_items - new_capacity;
        num_items = new_capacity;
    }

    pointer new_buffer = new T[new_capacity];
    for (size_type item_no = 0; item_no < num_items; ++item_no)
    {
        new_buffer[item_no] = (*this)[item_no + offset];
    }

    pointer old_buffer = _buffer;

    _buffer = new_buffer;
    _capacity = new_capacity;
    _front = (num_items % _capacity);
    _full = (num_items == _capacity);

    delete[] old_buffer;
}

#endif // CIRCULAR_BUFFER_H

Usuallly I init it like this

timed_temperature aTimedTemperature;
aTimedTemperature.dt =102019;
aTimedTemperature.temp=37.0;
CircularBuffer<timed_temperature> myCircularBufferedTemps = CircularBuffer<timed_temperature> (PLOT_RING_BUFFER_SIZE);
myCircularBufferedFilteredTemps.add(aTimedTemperature.dt);

So I tried to create a vector of CircularBuffer like this

std::vector<CircularBuffer<timed_temperature>> *myTempsVector = new std::vector< CircularBuffer<timed_temperature>(PLOT_RING_BUFFER_SIZE) >;

But obviously for all of you ☺️, it does not work !

I tried multiple things without success. So my question is only how can I declare in my header a member wich is a vector of my CircularBuffer<timed_temperature>(PLOT_RING_BUFFER_SIZE)

And how I access the myTempsVector[i].is_full() method of one element of the vector?

Thank you for your help.

Answer 1

You're confusing between CircularBuffer<timed_temperature> 's constructor and std::vector<T> constructor.

When you write:

std::vector< CircularBuffer<timed_temperature> >(PLOT_RING_BUFFER_SIZE)

It'll call std::vector's constructor with PLOT_RING_BUFFER_SIZE , trying to allocate PLOT_RING_BUFFER_SIZE different CircularBuffer<timed_temperature> using the default constructor.

Simply define your vector as such:

std::vector<CircularBuffer<timed_temperature>> myTempsVector;

Then add ( push_back ) any new instance you want, eg :

myTempsVector.push_back(CircularBuffer<timed_temperature> (PLOT_RING_BUFFER_SIZE));

Answer 2

You simply need to create a vector first...

std::vector<CircularBuffer<timed_temperature>> myTempsVector;

...and then put a value into it:

myTempsVector.push_back(CircularBuffer<timed_temperature>(PLOT_RING_BUFFER_SIZE));

While you're at it, you should not be performing manual memory management and storing a pointer unless you really need to . If you do need to store a vector through a pointer, consider using std::unique_ptr , or std::shared_ptr if std::unique_ptr doesn't work.