关于模版与class的问题，是VS 2013的问题吗？
本帖最后由 u011873969 于 2013-12-31 01:14:00 编辑 程序很简单，定义一个固定大小的数组，可以进行添加元素（因为初始时它是partially-filled）、清空、返回元素个数等操作，并且重载了<<操作符，但是在demonstration里进行到
cout <<
这一步的时候出现连接错误，搞了半天没明白是哪里出了问题，求大神指教！出错信息为
1>Demonstration.obj : error LNK2019: 无法解析的外部符号 "class std::basic_ostream<char,struct std::char_traits<char> > & __cdecl listsavitch::operator<<(class std::basic_ostream<char,struct std::char_traits<char> > &,class listsavitch::GenericList<int> const &)" (??6listsavitch@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV12@ABV?$GenericList@H@0@@Z)，该符号在函数 _main 中被引用
1>D:\ebook\C++\Problem Solving with C++\Chapter17, Templates\GenericList\Debug\GenericList.exe : fatal error LNK1120: 1 个无法解析的外部命令
下面是三个文件的代码：
genericlist.h
#ifndef GENERICLIST_H
#define GENERICLIST_H
#include <iostream>
using namespace std;
namespace listsavitch
{
template<class ItemType>
class GenericList
{
public:
GenericList(int max);
~GenericList();
int length() const;
void add(ItemType new_item);
bool full() const;
void erase();
friend ostream& operator <<(ostream& outs,
const GenericList<ItemType>& the_list);
private:
ItemType *item; // pointer to the dynamic array that holds the list.
int max_length; // max number of items allowed on the list.
int current_length; // number of items currently on the list.
};
}// listsavitch
#endif // GENERICLIST_H
#ifndef GENERICLIST_CPP
#define GENERICLIST_CPP
#include <iostream>
#include <cstdlib>
#include "genericlist.h"
using namespace std;
namespace listsavitch
{
//Uses cstdlib:
template<class ItemType>
GenericList<ItemType>::GenericList(int max) : max_length(max),
current_length(0)
{
item = new ItemType[max];
}
template<class ItemType>
GenericList<ItemType>::~GenericList()
{
delete []item;
}
template<class ItemType>
int GenericList<ItemType>::length() const
{
return (current_length);
}
// Uses iostream and cstdlib:
template<class ItemType>
void GenericList<ItemType>::add(ItemType new_item)
{
if (full())
{
cout << "Error: adding to a full list.\n";
exit(1);
}
else
{
item[current_length] = new_item;
current_length = current_length + 1;
}
}
template<class ItemType>
bool GenericList<ItemType>::full() const
{
return (current_length == max_length);
}
template<class ItemType>
void GenericList<ItemType>::erase()
{
current_length = 0;
}
// Uses iostream:
template<class ItemType>
ostream& operator <<(ostream& outs, const GenericList<ItemType>& the_list)
{
for (int i = 0; i < the_list.current_length; i++)
outs << the_list.item[i] << endl;
return outs;
}
}// listsavitch
#endif
#include <iostream>
#include "genericlist.h"
#include "genericlist.cpp"
using namespace std;
using namespace listsavitch;
int main()
{
GenericList<int> first_list(3);
first_list.add(1);
first_list.add(2);
cout << "first_list = \n"
<< first_list;
getchar();
}
[解决办法]
不是分离编译的原因，对于friend这个声明改成如下形式：
class GenericList定义中：
template<class T>
friend ostream& operator <<(ostream& outs,
const GenericList<T>& the_list);
