问题
I tried to google this but always come back with different issues. I am getting 3 unresolved externals when I try to compile this program:
1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall DynIntStack<char>::~DynIntStack<char>(void)" (??1?$DynIntStack@D@@QAE@XZ) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "public: void __thiscall DynIntStack<char>::pop(char &)" (?pop@?$DynIntStack@D@@QAEXAAD@Z) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "public: void __thiscall DynIntStack<char>::push(char)" (?push@?$DynIntStack@D@@QAEXD@Z) referenced in function _main
DynIntStack.h
/****************************************************************************
DynIntStack class.
Chad Peppers
This class creates a object for stacking nodes
In addition, there should be member functions to perform the following
operations:
- Push to the stack
- Pop to the stack
- Function to check if empty
****************************************************************************/
// Specification file for the DynIntStack class
#ifndef DYNINTSTACK_H
#define DYNINTSTACK_H
template <class T>
class DynIntStack
{
private:
// Structure for stack nodes
struct StackNode
{
T value; // Value in the node
StackNode *next; // Pointer to the next node
};
StackNode *top; // Pointer to the stack top
public:
// Constructor
DynIntStack()
{ top = NULL; }
// Destructor
~DynIntStack();
// Stack operations
void push(T);
void pop(T &);
bool isEmpty();
};
#endif
DynIntStack.cpp
/****************************************************************************
DynIntStack class.
Chad Peppers
This class creates a object for stacking nodes
In addition, there should be member functions to perform the following
operations:
- Push to the stack
- Pop to the stack
- Function to check if empty
****************************************************************************/
#include <iostream>
#include "DynIntStack.h"
using namespace std;
/*************************************************************************
Basic class constructor.
Input Parameters: Information to build the stack
Return Type: void
*************************************************************************/
template<class T>
DynIntStack<T>::~DynIntStack()
{
StackNode *nodePtr, *nextNode;
// Position nodePtr at the top of the stack.
nodePtr = top;
// Traverse the list deleting each node.
while (nodePtr != NULL)
{
nextNode = nodePtr->next;
delete nodePtr;
nodePtr = nextNode;
}
}
/*************************************************************************
Function to push an item in the stack
Input Parameters: T
Return Type: void
*************************************************************************/
template<class T>
void DynIntStack<T>::push(T num)
{
StackNode *newNode; // Pointer to a new node
// Allocate a new node and store num there.
newNode = new StackNode;
newNode->value = num;
// If there are no nodes in the list
// make newNode the first node.
if (isEmpty())
{
top = newNode;
newNode->next = NULL;
}
else // Otherwise, insert NewNode before top.
{
newNode->next = top;
top = newNode;
}
}
/*************************************************************************
Function to pop an item in the stack
Input Parameters: T
Return Type: void
*************************************************************************/
template<class T>
void DynIntStack<T>::pop(T &num)
{
StackNode *temp; // Temporary pointer
// First make sure the stack isn't empty.
if (isEmpty())
{
cout << "The stack is empty.\n";
}
else // pop value off top of stack
{
num = top->value;
temp = top->next;
delete top;
top = temp;
}
}
/*************************************************************************
Basic class deconstructor.
Input Parameters: None
Return Type: void
*************************************************************************/
template<class T>
bool DynIntStack<T>::isEmpty()
{
bool status;
if (!top)
status = true;
else
status = false;
return status;
}
main.cpp
#include <iostream>
#include "DynIntStack.h"
using namespace std;
int main(){
int value = 0;
char value2;
//DynIntStack<int> stack;
DynIntStack<char> stack1;
cout << "Pushing 1\n";
stack1.push('T');
stack1.pop(value2);
cout << value2;
system("pause");
return 0;
}
回答1:
You need to put all the template implementations that you have in your .cpp file in the header file, or in a file included by the header. And don't try to compile the implementation file. Some systems attempt to compile files with a .cpp suffix. The compiler needs to see the code in order to instantiate templates.
回答2:
at the bottom of DynIntStack.h, put
#include <DynIntStack.cpp>
what's happening is the compiler doesn't see the template implementation code so cannot emit anything for it.
回答3:
The most simplest solution to the problem is:
Wherever you want to include your template class e.g. "DynIntStack.h" instead do "DynIntStack.cpp". e.g. in your main.cpp above.
Simple as that, no need to change anything else.
来源：https://stackoverflow.com/questions/10271796/c-keep-getting-error-lnk2019-unresolved-external-symbol