复制构造函数中的C++向量数组

Question

我是新手复制构造函数,当我开始使用向量时似乎无法让它们工作.

//  ROBOT CLASS
class Robot {
    private:
        char *name;
        int size;

        int cmdCount;

        command *cmdList;
        char items[8][16];
        int resources[3]; // silver, gold, then platinum

    public: 
        Robot( );
        Robot(int num_of_cmds, const char *nm);
        Robot(const Robot &);
        ~Robot( );

        const char *get_name( );
        command get_command(int pos) const;
        void set_item(const char item[ ], int pos);
        const char *get_item(int pos);

};

//  ROBOT CONSTRUCTOR default
Robot::Robot( ) {

    //  Load Robot name
    cmdCount = 5;
    try {
        name = new char[11];
    }
    catch(std::bad_alloc) {
        cout << "Error allocating " << 11+1 << " bytes of memory\n";
        name = NULL;
    }

    if (name) {
        strcpy (name, "univac.dat");
    }

    //  Allocate memory for command array
    vector <command> cmdList[5];

};

//  ROBOT COPY CONSTRUCTOR
Robot::Robot(const Robot &from) {
    cmdCount = from.cmdCount;
    //  Load Robot name
    try {
        name = new char[11];
    }
    catch(std::bad_alloc) {
        cout << "Error allocating " << 11+1 << " bytes of memory\n";
        name = NULL;
    }

    if (name) {
        strcpy (name, from.name);
    }

    //  Allocate memory for command array
    vector <command> cmdList[5];

    for (int i=0; i < cmdCount;i++) {
        cmdList[i] = from.cmdList[i];
    }

    for (int i=0; i < 8; i++) {
        strcpy(items[i], from.items[i]);
    }

    for (int i=0; i < 3; i++) {
        resources[i] = from.resources[i];
    }

}    

编译时得到的错误是:

robot.cpp:在复制构造函数'Robot :: Robot(const Robot&)'中:robot.cpp:117:错误:'cmdList [i]中没有匹配'operator ='= (((命令)from-> Robot: :cmdList)+((unsigned int)(((unsigned int)i)*172u)))'/ usr /include/c++/4.4/bits/vector.tcc:156:注意:候选者是:std :: vector < _Tp,_Alloc>&std :: vector <_Tp,_Alloc> :: operator =(const std :: vector <_Tp,_Alloc>&)[with _Tp = command,_Alloc = std :: allocator]

我如何在复制构造函数中复制矢量数组？

Answer 1

在您的类中,您声明一个成员变量:

command *cmdList;

但是在每个构造函数中,都声明了一个具有相同名称的局部变量:

vector <command> cmdList[5];

实际上,您需要成员变量的类型为vector<command>:

//  ROBOT CLASS
class Robot {
    private:
…
        std::vector<command> cmdList;    
…
};

然后,在默认构造函数中,您可以为其分配内存.您不一定要这样做,具体取决于您以后如何使用它.

//  ROBOT CONSTRUCTOR default
Robot::Robot( ) :cmdList(5) {
… // no mention of cmdList in the body required    
};

最后,在复制构造函数中,复制它:

//  ROBOT COPY CONSTRUCTOR
Robot::Robot(const Robot &from) : cmdList(from.cmdList) {
… // no mention of cmdList in the body required
}  

替代方法:作为替代方案,如果您选择不在构造函数中使用初始化列表,则可以执行以下操作:

Robot::Robot() {
…
    cmdList = std::vector<command>(5);
    // or cmdList.resize(5);
…
}

Robot::Robot(const Robot &from) {
… 
    cmdList = from.cmdList;
…
}  

额外信用:如果您进行了以下更改,那么您可能根本不需要复制构造函数!你也不需要析构函数或赋值运算符:

 class Robot {
    private:
        std::string name;
        int size;

        int cmdCount;

        std::vector<command> cmdList;
        char items[8][16];
        int resources[3]; // silver, gold, then platinum

    public: 
        Robot( );
        Robot(int num_of_cmds, const char *nm);

        const char *get_name( ) { return name.c_str(); }
        command get_command(int pos) const { return cmdList[pos]; }
        void set_item(const char item[ ], int pos);
        const char *get_item(int pos);
};