c++ - 模板复制构造函数出错

Question

我尝试为列表创建复制构造函数。该列表将所有变量作为私有(private)成员。模板中的构造函数有什么特别之处，所以这不起作用吗？

我收到这些错误:

   1>          consoleapplication1\consoleapplication1\circulardoubledirectedlist.h(52) : while compiling class template member function 'CircularDoubleDirectedList<int>::CircularDoubleDirectedList(const CircularDoubleDirectedList<int> &)'
    1>          consoleapplication1\consoleapplication1\testdeepcopyingoflist.cpp(25) : see reference to function template instantiation 'CircularDoubleDirectedList<int>::CircularDoubleDirectedList(const CircularDoubleDirectedList<int> &)' being compiled
    1>          consoleapplication1\consoleapplication1\testdeepcopyingoflist.cpp(24) : see reference to class template instantiation 'CircularDoubleDirectedList<int>' being compiled
    1>consoleapplication1\consoleapplication1\circulardoubledirectedlist.h(57): error C2039: 'dir' : is not a member of 'CircularDoubleDirectedList<int>'
    1>consoleapplication1\consoleapplication1\circulardoubledirectedlist.h(62): error C2662: 'void CircularDoubleDirectedList<int>::changeDirection(void)' : cannot convert 'this' pointer from 'const CircularDoubleDirectedList<int>' to 'CircularDoubleDirectedList<int> &'
    1>          Conversion loses qualifiers
    1>consoleapplication1\consoleapplication1\circulardoubledirectedlist.h(68): error C2662: 'void CircularDoubleDirectedList<int>::moveCurrent(void)' : cannot convert 'this' pointer from 'const CircularDoubleDirectedList<int>' to 'CircularDoubleDirectedList<int> &'
    1>          Conversion loses qualifiers
    1>consoleapplication1\consoleapplication1\circulardoubledirectedlist.h(71): error C2662: 'void CircularDoubleDirectedList<int>::changeDirection(void)' : cannot convert 'this' pointer from 'const CircularDoubleDirectedList<int>' to 'CircularDoubleDirectedList<int> &'
    1>          Conversion loses qualifiers

我的代码:

template <typename T>
CircularDoubleDirectedList<T>::CircularDoubleDirectedList(const CircularDoubleDirectedList<T>& other){

    bool changeDir;

    if (other.getCurrentDirection == ICircularDoubleDirectedList::FORWARD){
        changeDir = false;
    }
    else{
        changeDir = true;
        other.changeDirection();
    }

    int size = other.size();
    for (int i = 0; i < size; i++){
        this->addAtCurrent(other.getElementAtCurrent());
        other.moveCurrent();
    }
    if (changeDir){
        other.changeDirection();
    }
    this->currentDirection = other.getCurrentDirection();

}

Answer 1

您的复制构造函数(正确地)有一个 const 引用参数。但是，看起来您正试图在参数上调用非 const 成员:

other.changeDirection(); // this looks like a non-const operation
....

other.moveCurrent();     // this looks like a non-const operation

等复制构造函数修改从 复制的东西没有多大意义，但如果你真的需要它，那么你需要参数是非 const 引用.

或者，如果这些成员函数不修改对象，则将它们设为const。

请注意，这与模板无关。