求助 关于模板类中的重载运算符的友元函数
[root@localhost genDLLst]# g++ -o genDLLst2 genDLLst2.cpp
genDLLst2.cpp:41: warning: friend declaration `std::ostream& operator < <(std::ostream&, const DoublyLinkedList <T> &) ' declares a non-template function
genDLLst2.cpp:41: warning: (if this is not what you intended, make sure the function template has already been declared and add <> after the function name here) -Wno-non-template-friend disables this warning
源代码如下:
#include <iostream>
using namespace std;
template <typename T>
class DLLNode {
public:
DLLNode() {
next = prev = 0;
}
DLLNode(const T& el, DLLNode *n = 0, DLLNode *p = 0) {
info = el; next = n; prev = p;
}
T info;
DLLNode *next, *prev;
};
template <typename T>
class DoublyLinkedList {
public:
DoublyLinkedList() {
head = tail = 0;
}
void addToDLLTail(const T&);
T deleteFromDLLTail();
~DoublyLinkedList() {
clear();
}
bool isEmpty() const {
return head == 0;
}
void clear();
void setToNull() {
head = tail = 0;
}
void addInMiddle(const T&);
void addToDLLHead(const T&);
T deleteFromDLLHead();
T& firstEl();
T* find(const T&) const;
void run();
protected:
DLLNode <T> *head, *tail;
friend ostream& operator < <(ostream&, const DoublyLinkedList <T> &);
};
template <typename T>
ostream& operator < <(ostream& out, const DoublyLinkedList <T> & dll) {
DLLNode <T> *tmp;
for (tmp = dll.head; tmp != 0; tmp = tmp-> next)
out < < tmp-> info < < ' ';
return out;
}
int main()
{
return 0;
}
[解决办法]
friend ostream& operator < <(ostream&, const DoublyLinkedList <T> &)
{
DLLNode <T> *tmp;
for (tmp = dll.head; tmp != 0; tmp = tmp-> next)
out < < tmp-> info < < ' ';
return out;
}
friend声明时就地实现。
