「從這裏需要」的錯誤聲明列表

Question

我想聲明這樣一個列表的列表清單：

List_vector<List_vector<int> > multilist; 

但是Eclipse強調了上述聲明，並給出了這個錯誤：

required from here

部分List_vector實現：

template<class T> 
class List_vector: public Linear_list<T, int> { 
public: 
    typedef typename Linear_list<T, int>::value_type value_type; 
    typedef typename Linear_list<T, int>::position position; 

    List_vector(); 
    List_vector(int); 
    List_vector(const List_vector<T>&); 
    ~List_vector(); 
private: 
    void change_dimension_(T*&, int, int); 
    value_type* elements_; 
    int length_; // the length of the list 
    int array_dimension_; // array's dimension 
}; 

編譯器輸出：

g++ -O3 -Wall -c -fmessage-length=0 -o multilista.o "..\\multilista.cpp" 
In file included from ..\multilista.cpp:1:0: 
..\list_vector.h: In instantiation of 'List_vector<T>::~List_vector() [with T = List_vector<int>]': 
..\multilista.cpp:16:32: required from here 
..\list_vector.h:78:5: warning: deleting object of polymorphic class type List_vector<int>' which has non-virtual destructor might cause undefined behaviour [-Wdelete-non-virtual-dtor] 
..\list_vector.h: In member function 'List_vector<T>::value_type List_vector<T>::read(List_vector<T>::position) const [with T = int; List_vector<T>::value_type = int; List_vector<T>::position = int]': 
..\list_vector.h:136:1: warning: control reaches end of non-void function [-Wreturn-type] 
..\list_vector.h: In member function 'List_vector<T>::value_type List_vector<T>::read(List_vector<T>::position) const [with T = List_vector<int>; List_vector<T>::value_type = List_vector<int>; List_vector<T>::position = int]': 
..\list_vector.h:136:1: warning: control reaches end of non-void function [-Wreturn-type] 
g++ -O3 -Wall -c -fmessage-length=0 -o tester.o "..\\tester.cpp" 
g++ -o Lista.exe tester.o multilista.o 

Answer 1

In file included from ..\multilista.cpp:1:0: 
..\list_vector.h: In instantiation of 'List_vector<T>::~List_vector() [with T = List_vector<int>]': 
..\multilista.cpp:16:32: required from here 
..\list_vector.h:78:5: warning: deleting object of polymorphic class type 'List_vector<int>' which has non-virtual destructor might cause undefined behaviour [-Wdelete-non-virtual-dtor] 

如果你打算從Linear_List推導，你應該考慮的析構函數虛擬的，就像它說。這只是一個警告，只有你知道它是否真的需要（沒有足夠的代碼粘貼來判斷）。

..\list_vector.h: In member function 'List_vector<T>::value_type List_vector<T>::read(List_vector<T>::position) const [with T = int; List_vector<T>::value_type = int; List_vector<T>::position = int]': 
..\list_vector.h:136:1: warning: control reaches end of non-void function [-Wreturn-type] 

您還沒有貼上了List_vector::read的代碼，但它似乎是做錯了什麼：該功能的每一個路徑應返回List_vector::value_type（除非它拋出一個異常），但你讓控制沒有做任何事情就達到目的。

..\list_vector.h: In member function 'List_vector<T>::value_type List_vector<T>::read(List_vector<T>::position) const [with T = List_vector<int>; List_vector<T>::value_type = List_vector<int>; List_vector<T>::position = int]': 
..\list_vector.h:136:1: warning: control reaches end of non-void function [-Wreturn-type]