1

我有以下代码。

class Wave {

int m_length;
data_type * m_data;

public:

    Wave(){
        blah...blah...blah
        m_data = NULL;
        m_length = 0;
        cout << "Wave " << this << " created on " << m_data << " with m_length " <<  m_length << endl;
    }

    Wave(int len, data_type data){
        blah...blah...blah
        if (len) {
            m_length = len;
            m_data = new data_type [m_length];
        } else {
            m_length = 0;
            m_data = NULL;
        }
        cout << "Wave " << this << " created on " << m_data << " with m_length " <<  m_length << endl;
    }



    ~Wave() 
    {
    cout << "Wave " << this << " destructor  on " << m_data << " started ";
        if (m_length) delete[] m_data;
    cout << "and finished " << endl;
    };        





    Wave & operator+= (const Wave wave){
    cout << __FUNCTION__ << ":" << __LINE__ << " m_length " << m_length << endl;
    if (NULL != m_data){
        data_type * tBuf = new data_type [m_length + wave.Length()];
        copy (wave.begin(),wave.end(), copy (begin(),end(),iterator(tBuf)));
        cout << "Wave " << this << " data on " << m_data << " moved onto " << tBuf;
        delete[] m_data;
        m_data = tBuf;
        cout << " and deleted" << endl;
    } else {
        m_data = new data_type [wave.Length()];
        copy (wave.begin(), wave.end(), begin());
        cout << "Wave " << this << " data created on " << m_data << " of length " <<  wave.Length() << endl;
    }
    m_length += wave.Length();
    cout << __FUNCTION__ << ":" << __LINE__ << " m_length " << m_length << endl;
    return *this;
    };

}


main(){

blah..blah..blah

Wave sample;

for (......) {

    cout << pulseNum << "-th High part: " << pulse->first << endl;
    Wave tSample(x,y);
    blah.blah.blah

    sample += tSample;

    cout << endl << pulseNum++ << "-th Low part: " << pulse->second << endl;
    tSample = Wave(a,b);
    blah.blah.blah

    sample += tSample;
}

}

下面是执行此代码的日志

Wave 0x28fe34 created on 0 with m_length 0
0-th High part: 220
Wave 0x28fe54 created on 0xc60f00 with m_length 207
operator+=:211 m_length 0
Wave 0x28fe34 data created on 0xc610a8 of length 207
operator+=:230 m_length 207
Wave 0x28fe9c destructor  on 0xc60f00 started and finished

0-th Low part: 320
Wave 0x28febc created on 0xc61250 with m_length 301
Wave 0x28febc destructor  on 0xc61250 started and finished
operator+=:211 m_length 207
Wave 0x28fe34 data on 0xc610a8 moved to 0xc61250 and deleted 
operator+=:230 m_length 508
Wave 0x28fee0 destructor  on 0xc61250 started and finished

Wave 0x28fe54 destructor  on 0xc61250 started and finished

对我来说最奇怪的是析构函数的调用次数比构造函数的调用次数多。此外，它被调用用于以前从未构造过的对象，而是用于相同的数据地址。
怎么可能？

4

2 回答 2

8

Wave有一个编译器生成的复制构造函数，你看不到它的输出。

例如，调用此复制构造函数来构造作为 的参数的对象Wave & operator+= (const Wave wave)。

于 2012-10-18T11:25:08.770 回答
2

如果您想简化代码，只需定义一个std::vector<data_type> m_data数据成员，而不是使用原始指针 ( data_type * m_data)。

这样，编译器会自动为你的类生成正确的复制构造函数、复制操作符=（以及移动语义）和析构函数（自动生成的复制构造函数、复制操作符=和析构函数将操作成员- 明智的，例如自动生成的复制构造函数将为您的类的每个数据成员调用复制构造函数）。

分配数据，而不是：

m_data = new data_type [m_length];

采用：

m_data.resize(m_length);

您还可以摆脱m_length数据成员，因为它std::vector知道自己的大小（您可以通过std::vector::size()方法访问它）。

请注意，std::vector将其所有元素存储在一个连续的内存区域中（如new[]）；您可以使用 访问该区域的开头&m_data[0]。

于 2012-10-18T11:33:26.390 回答