C ++（gcc）：未定义的引用`Stack< int> :: Stack（int）' [英] C++ (gcc): undefined reference to `Stack<int>::Stack(int)'

问题描述

可能重复：

我已经努力了一段时间，我在这里看看几个问题，但是对C ++新的我不能理解我错在哪里。

这是代码，我从这个页面，并试图使其工作，但到目前为止我还没有幸运：

stack.h

  #ifndef STACK_H 
 #define STACK_H 
 template< class T> ; 
 class Stack {
 public：
 Stack（int n）; 
〜Stack（）{delete [] s; }; 
 private：
 T * s; 
 int _top; 
 int _size; 
}; 
 #endif // STACK_H 
  

stack.cpp p>

  #includestack.h
 template< class T> 
 Stack< T> :: Stack（int n）{
 _size = n; 
 _top = -1; 
 s = new T [_size]; 
} 
  

main.cpp
$ b

  #include< iostream> 
 #includestack.h
 using namespace std; 
 int main（）{
 Stack< int> s（10）; //未定义的引用`Stack< int> :: Stack（int）'
 return 0; 
} 
  

当我编译（gcc 4.5.2），我得到一个错误：未定义引用Stack< int> :: Stack（int）。我试过几件事，但没有任何真正的知识支持我做什么。

解决方案

在cpp中只能有一个模板类定义文件，如果它是一个专门的定义 - 即你知道 T 是什么。

这里，你的模板类的所有定义都必须放在头文件中。编译器必须知道这些每次一个新的实例被声明或定义，因为类型，从而行为，改变。 cpp文件中的定义意味着一个不同的翻译单元，所以编译器不可能知道每一个 T 的行为，你试图应用到你的模板。 p>

Possible Duplicate:
Why can templates only be implemented in the header file?

I've struggled with this for a while, and I've taken a look to several questions here, but being new to C++ I haven't been able to understand where I am wrong.

Here is the code, I took it from this page and tried to make it work, but so far I haven't been lucky:

stack.h

#ifndef STACK_H
#define STACK_H
template <class T>
class Stack {
  public:
    Stack(int n);
    ~Stack() { delete[] s; };
  private:
    T* s;
    int _top;
    int _size;
};
#endif // STACK_H

stack.cpp

#include "stack.h"
template <class T>
Stack<T>::Stack(int n) {
  _size = n;
  _top = -1;
  s = new T[_size];
}

main.cpp

#include <iostream>
#include "stack.h"
using namespace std;
int main() {
  Stack<int> s(10); // undefined reference to `Stack<int>::Stack(int)'
  return 0;
}

When I compile (gcc 4.5.2) I get one error: undefined reference to Stack<int>::Stack(int). I've tried several things but without any real knowledge to support what I do. I will be really thankful if somebody can explain me what's going on.

解决方案

You can only have a template class definition in a cpp file if it's a specialized definition - i.e. you know what T is.

Other than that, and your case belongs here, all definitions of your template class have to go in the header file. The compiler has to know about these each time a new instance is declared or defined because the type, and thus the behavior, changes. Definitions in a cpp file would mean a different translation unit, so the compiler couldn't possibly know about the behavior for every single T you try to apply to your template.

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