c++ - 在类中初始化动态内存数组

Question

我是 C++ 编程新手，这可能是一个微不足道的问题，但我需要在一个类中构造一个可变大小的数组并将文本文件数据传输到其中，见下文。这里HISTORYFile >> ClusterCoord[i];似乎可以很好地接收信息，但是当我尝试通过以下方式访问主程序中的信息时，

cout << CoordClassExample.ClusterCoord[1] << "\n";

我得到一个总线错误。如果可以的话请帮忙！

class CoordClass{
public:
    int Entries;
    double * ClusterCoord;
    void set_valuesCoord(ifstream &HISTORYFile,int MolAtomNum, int MolNum);
};

void CoordClass::set_valuesCoord(ifstream& HISTORYFile,int MolAtomNum, int MolNum) {
    Entries=MolAtomNum*MolNum;
    double *ClusterCoord = new double [Entries];

    for (int i=0;i<Entries;i++) {
        HISTORYFile.ignore(1000,'\n');      
            HISTORYFile >> ClusterCoord[i];
        cout << ClusterCoord[i] << "\n";
            HISTORYFile.ignore(1000,'\n');
    }
}

Answer 1

You have a leak in the set_valuesCoord() function if you call the function twice, unless you somewhere release the resources. That's not the problem but it's a problem. Use a std::vector<>.

class CoordClass {
    // ...
    std::vector<double> ClusterCoord;  // instead of double *ClusterCoord
    // ...
};

What might be the problem is that you don't check whether the double parsed properly. If it didn't then you're accessing uninitialized memory, and that leads to undefined behaviour.

void CoordClass::set_valuesCoord(...)
{
    // ...
    double cluster_coord = 0;
    if( HISTORYFile >> cluster_coord )
        ClusterCoord.push_back(cluster_coord);
    else
        std::cerr << "Error parsing cluster coord.\n";
    // ...
}

Answer 2

作为一个练习，展示vector不会泄漏的方式：

进一步的变化是删除 Entries 并使用ClusterCoord.size().

class CoordClass{
public:
    int Entries;
    std::vector<double> ClusterCoord;
    void set_valuesCoord(ifstream &HISTORYFile,int MolAtomNum, int MolNum);
};

void CoordClass::set_valuesCoord(ifstream& HISTORYFile,int MolAtomNum, int MolNum) {
    Entries=MolAtomNum*MolNum;
    ClusterCoord.resize(Entries);

    for (int i=0;i<Entries;i++) {
        HISTORYFile.ignore(1000,'\n');      
            HISTORYFile >> ClusterCoord[i];
        cout << ClusterCoord[i] << "\n";
            HISTORYFile.ignore(1000,'\n');
    }
}