很简单的c++问题 出现链接问题 想不明白
学习c++ primer书中 关于vector 自己实现一下 发现 类里面具体实现如果放在类头文件下编译通过 不放在头文件下单起 x.cpp然后包含头文件就不行 出错 说什么找不到 具体看实例
这是vector.h

C/C++ code

#include<memory>#include<iostream>//using namespace std;using std::cout; using std::endl;template<class Type>class Vector{public:    Vector():elments(0),first_free(0),end(0){};    void push_back_new(const Type&);private:    void realloc();    static std::allocator<Type> alloc;    Type *elments;    Type *first_free;    Type *end;}; 

vector.cpp

C/C++ code

#include"vector.h"#include<algorithm>using std::allocator;template <class T> allocator<T> Vector<T>::alloc;using std::max;using std::uninitialized_copy;template<class Type> void Vector<Type>::realloc(){    std::ptrdiff_t size = first_free - elments;    std::ptrdiff_t newcapacity = 2* max(size,0);    Type *newelments = alloc.allocate(newcapacity);    uninitialized_copy(elments,first_free,newelments);    for(Type *p = first_free;p != elments;)        alloc.destroy(--p);    if(elments)        alloc.deallocate(elments,end-elments);    elments = newelments;    first_free = elments + size;    end = elments + newcapacity;}template<class Type> void Vector<Type>::push_back_new(const Type& t){    if(first_free == end)        realloc();    alloc.construct(first_free,t);    ++first_free;}

main.cpp

C/C++ code

#include"vector.h"int main (){    Vector<int>vec;    vec.push_back_new(5);    vec.push_back_new(5);    vec.push_back_new(5);    vec.push_back_new(5);    vec.push_back_new(5);}

编译器vs2010
错误如下
1>main.obj : error LNK2019: 无法解析的外部符号 "public: void __thiscall Vector<int>::push_back_new(int const &)" (?push_back_new@?$Vector@H@@QAEXABH@Z)，该符号在函数 _main 中被引用
1>E:\STUDY\C++\Code\vs2010\allocator_vector_20120325\Debug\allocator_vector_20120325.exe : fatal error LNK1120: 1 个无法解析的外部命令

如果把前两个文件合一 就能编译通过但是会出现诡异的问题 要求我中断或者继续不知道是什么错误

C/C++ code

#include<memory>#include<iostream>//using namespace std;using std::cout; using std::endl;template<class Type>class Vector{public:    Vector():elments(0),first_free(0),end(0){};    void push_back_new(const Type&);private:    void realloc();    static std::allocator<Type> alloc;    Type *elments;    Type *first_free;    Type *end;}; #include<algorithm>using std::allocator;template <class T> allocator<T> Vector<T>::alloc;/*这句非常不明白 按照原书代码不加这句不行我不明白的是 alloc明明是我类里定义的 为什么还得加这句那这句什么意思呢 作用呢*/using std::max;using std::uninitialized_copy;template<class Type> void Vector<Type>::realloc(){    std::ptrdiff_t size = first_free - elments;    std::ptrdiff_t newcapacity = 2* max(size,0);    Type *newelments = alloc.allocate(newcapacity);    uninitialized_copy(elments,first_free,newelments);    for(Type *p = first_free;p != elments;)        alloc.destroy(--p);    if(elments)        alloc.deallocate(elments,end-elments);    elments = newelments;    first_free = elments + size;    end = elments + newcapacity;}template<class Type> void Vector<Type>::push_back_new(const Type& t){    if(first_free == end)        realloc();    alloc.construct(first_free,t);    ++first_free;}

完全一样的代码

问题出来了 1为什么设计实现分离就出错呢 2 合到一起出的是什么错呢 3 我注视的那一段 干什么用的呢
下面付原书代码 求解答原书设计实现分离的话也是一样的问题（改完我包含头了）

C/C++ code

 
 #include <iostream>using std::cout; using std::endl;#include <memory>// psuedo-implementation of memory allocation strategy for a vector-like classtemplate <class T> class Vector {public:    Vector(): elements(0), first_free(0), end(0) { }    void push_back(const T&);    size_t size() const { return first_free - elements; }    size_t capacity() const { return end - elements; }    // . . .    T& operator[](size_t n) { return elements[n]; }    const T& operator[](size_t n) const { return elements[n]; }private:    static std::allocator<T> alloc; // member to handle allocation    void reallocate(); // get more space and copy existing elements    T* elements;       // pointer to first element in the array    T* first_free;     // pointer to first free element in the array    T* end;            // pointer to one past the end of the array    // . . .};#include <algorithm>using std::allocator;template <class T> allocator<T> Vector<T>::alloc;using std::max;using std::uninitialized_copy;template <class T> void Vector<T>::reallocate(){    // compute size of current array and allocate space for twice as many elements    std::ptrdiff_t size = first_free - elements;     std::ptrdiff_t newcapacity = 2 * max(size, 1);    // allocate space to hold newcapacity number of elements of type T    T* newelements = alloc.allocate(newcapacity);     // construct copies of the existing elements in the new space    uninitialized_copy(elements, first_free, newelements);    // destroy the old elements in reverse order    for (T *p = first_free; p != elements; /*empty*/ )        alloc.destroy(--p);        // deallocate cannot be called on a 0 pointer    if (elements)        // return the memory that held the elements        alloc.deallocate(elements, end - elements);    // make our data structure point to the new elements    elements = newelements;    first_free = elements + size;    end = elements + newcapacity;}template <class T> void Vector<T>::push_back(const T& t){    // any space left?    if (first_free == end)      reallocate(); // gets more space and copies existing elements to it    // construct a copy t in the element to which first_free points    alloc.construct(first_free, t);      ++first_free;}int main(){    Vector<int> vi;    for (int i = 0; i != 10; ++i) {      vi.push_back(i);      cout << vi[i] << endl;    }    for (int i = 0; i != 10; ++i)      cout << vi[i] << endl;    return 0;}

新手什么也不懂 欢迎大家帮帮忙 好郁闷


[解决办法]
c++ class template要求实现和声明必须在一个文件当中。就是一个规则而已。这也是类模板实现的通常做法。编译器就是这么支持的，否则编译不能通过。