问题描述

关于c++ error LNK2019: unresolved external symbol 问题

我运行了一个程序，报出如下错：
Error 1 error LNK2019: unresolved external symbol ""public: __thiscall CircList::CircList(int)"" (??0?$CircList@N@@QAE@H@Z) referenced in function _wmain
Error 2 error LNK2019: unresolved external symbol ""public: __thiscall CircList::~CircList(void)"" (??1?$CircList@N@@QAE@XZ) referenced in function _wmain
Error 3 error LNK2019: unresolved external symbol ""public: struct CircListNode * __thiscall CircList::Locate(int)"" (?Locate@?$CircList@N@@QAEPAU?$CircListNode@N@@H@Z) referenced in function ""void __cdecl Josephus(class CircList &intintint)"" (??$Josephus@N@@YAXAAV?$CircList@N@@HHH@Z)

Error 4 error LNK1120: 3 unresolved externals
程序代码如下：

 #ifndef CIRCLIST_H_#define CIRCLIST_H_template <class T>struct CircListNode{    T data;    CircListNode<T> * link;};template <class T>class CircList{private:    CircListNode<T> * first;public:    CircList(){}    CircList(int i);    ~CircList();    CircListNode<T> * Locate(int i);};#endif

 #include ""stdafx.h""#include ""circList.h""#include <iostream>using namespace std;template<class T>CircList<T>::CircList(int i){    T value;    first = new CircListNode < T > ;    for (int j = 0; j < i; j++)    {        CircListNode<T> * newNode = new CircListNode < T > ;        cout << ""请输入第"" << j + 1 << ""个节点的值："";        getline(cin value);        newNode->data = valude;        newNode->link = first->link;        first->link = newNode;    }    cout << ""一个包含"" << i << ""个节点的循环表建立成功！"" << endl;}template<class T>CircList<T>::~CircList(){    CircListNode<T> * q;    while (first->link != NULL)    {        q = first->link;        first->link = q->link;        delete q;    }    delete first;}template<class T>CircListNode<T> * CircList<T>::Locate(int i){    CircListNode<T> * current = new CircListNode < T > ;    if (current == NULL)    {        cout << ""内存分配错误！"" << endl;        return NULL;    }    else    {        current = first->link;        for (int j = 1; j < i - 1; j++)            current = current->link;        return current;    }}

 // ex2-5.cpp : Defines the entry point for the console application.//#include ""stdafx.h""#include <iostream>#include ""circList.h""using namespace std;template<class T>void Josephus(CircList<T> & js int n int s int m);int _tmain(int argc _TCHAR* argv[]){    int n s m;    cout << ""请输入游戏人数、开始位置和报数间隔： "";    cin >> n >> s >> m;    CircList<double> clist(n);    Josephus(clist n s m);    return 0;}template<class T>void Josephus(CircList<T> & js int n int s int m){    CircListNode<T> * p = js.Locate(s) *pre = NULL;    for (int i = 0; i < n - 1; i++)    {        for (int j = 1; j < m; j++)        {            pre = p;            p = p->link;        }        cout << ""出列的人是"" << p->data << endl;        pre->link = p->link;        p = pre->link;    }}

求大神解释一下，谢谢了

解决方案

模板函数的定义原则上应该和声明放在同一个文件里。你的这里，虽然代码里有

 #include ""circList.h""

但是编译器将模板实例化的时候找不到构造和析构函数的定义，因此才出现unresolved external symbol的问题。

你可以把你的函数定义加在头文件里，你也可以上网搜一下其他的模板函数的写法，比如我一直认为很别扭的#include ""xxx.cpp"" ...

解决方案二：
main.obj : error LNK2019: unresolved external symbol ""public: virtual __thiscall CvSVM::~CvSVM(void)"" (??1CvSVM@@UAE@XZ) referenced in function _main
1>main.obj : error LNK2019: unresol......
答案就在这里：error LNK2019: unresolved external symbol 问题

解决方案三：
CircList定义有问题

解决方案四：
模板函数声明在circList.h，而实现在circList.cpp，编译就会报错，原因为：模板函数在编译中就会实例化，把声明和定义分开，在一个编译单元内，及头文件展开后。在编译的时候虽然能找到函数声明，但是没有定义。
参考：http://blog.sina.com.cn/s/blog_5c8b05eb0100xzjg.html