Qt ------ 自定义QVector<T>中的T

#ifndef FREQUENCYSPECTRUM_H
#define FREQUENCYSPECTRUM_H

#include <QtCore/QVector>

/**
 * Represents a frequency spectrum as a series of elements, each of which
 * consists of a frequency, an amplitude and a phase.
 */
class FrequencySpectrum {
public:
    FrequencySpectrum(int numPoints = );

    struct Element
    {
        Element()
        :   frequency(0.0), amplitude(0.0), phase(0.0), clipped(false)
        { }

        /**
         * Frequency in Hertz
         */
        qreal frequency;

        /**
         * Amplitude in range [0.0, 1.0]
         */
        qreal amplitude;

        /**
         * Phase in range [0.0, 2*PI]
         */
        qreal phase;

        /**
         * Indicates whether value has been clipped during spectrum analysis
         */
        bool clipped;
    };

    typedef QVector<Element>::iterator iterator;
    typedef QVector<Element>::const_iterator const_iterator;

    void reset();

    int count() const;
    Element& operator[](int index);
    const Element& operator[](int index) const;
    iterator begin();
    iterator end();
    const_iterator begin() const;
    const_iterator end() const;

private:
    QVector<Element> m_elements;

};

#endif // FREQUENCYSPECTRUM_H

#include "frequencyspectrum.h"

FrequencySpectrum::FrequencySpectrum(int numPoints)
    :   m_elements(numPoints)//等于m_elements.resize(numPoints);
{

}

void FrequencySpectrum::reset()
{
    iterator i = begin();
    for ( ; i != end(); ++i)
        *i = Element();
}

int FrequencySpectrum::count() const
{
    return m_elements.count();
}

FrequencySpectrum::Element &FrequencySpectrum::operator[](int index)
{
    return m_elements[index];
}

const FrequencySpectrum::Element &FrequencySpectrum::operator[](int index) const
{
    return m_elements[index];
}

FrequencySpectrum::iterator FrequencySpectrum::begin()
{
    return m_elements.begin();
}

FrequencySpectrum::iterator FrequencySpectrum::end()
{
    return m_elements.end();
}

FrequencySpectrum::const_iterator FrequencySpectrum::begin() const
{
    return m_elements.begin();
}

FrequencySpectrum::const_iterator FrequencySpectrum::end() const
{
    return m_elements.end();
}