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Closed 10 years ago.
Possible Duplicate:
Why can templates only be implemented in the header file?
Undefined reference to function template when used with string (GCC)
C++ templates, undefined reference
I feel I'm missing something linking a C++ project.
I'm not sure if the problem is in the header sources or includes so I made a minimal code sample to demonstrate it.
Main module
minmain.cpp:
#include <stdio.h>
#include <vector>
#include <string>
#include "nodemin.h"
using namespace std;
int main()
{
// Blist libs are included
Node<int>* ndNew = ndNew->Root(2);
return 0;
}
Header file
nodemin.h:
#ifndef NODETEMP_H_
#define NODETEMP_H_
using namespace std;
template<class T>
class Node
{
protected:
Node* m_ndFather;
vector<Node*> m_vecSons;
T m_Content;
Node(Node* ndFather, T Content);
public:
// Creates a node to serve as a root
static Node<T>* Root(T RootTitle);
};
#endif
node module
nodemin.cpp:
#include <iostream>
#include <string.h>
#include <vector>
#include "nodemin.h"
using namespace std;
template <class T>
Node<T>::Node(Node* ndFather, T Content)
{
this->m_ndFather = ndFather;
this->m_Content = Content;
}
template <class T>
Node<T>* Node<T>::Root(T RootTitle) { return(new Node(0, RootTitle)); }
Compile line:
#g++ -Wall -g mainmin.cpp nodemin.cpp
Output:
/tmp/ccMI0eNd.o: In function `main':
/home/******/projects/.../src/Node/mainmin.cpp:11: undefined reference to`Node<int>::Root(int)'
collect2: error: ld returned 1 exit status
I tried compiling into objects but the linking still failed.
Add template class Node<int>; to nodemin.cpp:
#include <iostream>
#include <string.h>
#include <vector>
#include "nodemin.h"
using namespace std;
template <class T>
Node<T>::Node(Node* ndFather, T Content)
{
this->m_ndFather = ndFather;
this->m_Content = Content;
}
template <class T>
Node<T>* Node<T>::Root(T RootTitle) { return(new Node(0, RootTitle)); }
template class Node<int>;
Related
I am attempting to create a templated vector class, but upon compilation I am receiving an error of
def.hpp:3:1: error: 'TempVector' does not name a type
I keep referring to reference material and my syntax and handling of the header file declaration and definition (.h and .hpp) seem right to me, but I can not figure out what I am overlooking.
Below is the three files I am working with, thank you.
driver.cpp:
#include <iostream>
#include <string>
#include "dec.h"
using namespace std;
int main() {
TempVector <int> v1;
cout<<"ran successfully"<<endl;
}
dec.h:
#ifndef DEC_H
#define DEC_H
#include <iostream>
#include <utility>
// Declaration of class Vector
template <typename T>
class TempVector {
public:
TempVector ();
private:
T* array;
static const unsigned int spare = 10;
};
#include "def.hpp"
#endif
def.hpp:
template <typename T>
TempVector<T>::TempVector () {
std::cout<<"ran successfully";
}
I have been stuck for a while now and am unable to figure out why I am getting this compile error.
Node.hpp
#ifndef H1
#define H1
template <typename T>
class Node{
private:
T data;
public:
T getData();
};
#endif
Node.cpp
#include "Node.hpp"
template<typename T>
T Node<T>::getData(){
return data;
}
main.cpp
#include <bits/stdc++.h>
#include "Node.hpp"
using namespace std;
int main()
{
Node<int> *n = new Node<int>();
cout << n->getData();
}
g++ main.cpp Node.cpp -std=c++17
O/P: main.cpp:(.text+0x24): undefined reference to `Node::getData()'collect2: error: ld returned 1 exit status
PS: I tried the same thing without any template (use a primitive datatype instead), I do not get any error. So this probably has got something to do with the typename. Would be great if someone could tell me what is wrong here.
Node.hpp
#ifndef H1
#define H1
template <typename T>
class Node{
private:
T data;
public:
T getData() { return data; }
};
//or define it here
#endif
Then no need for Node.cpp. You might want to consider returning a const reference if your use-case allows it as T now requires a copy constructor. Although maybe that's what you want, I don't know your use-case.
See Why can template only be defined in header files
This question already has answers here:
Why can templates only be implemented in the header file?
(17 answers)
Closed 7 years ago.
I have a templated class named DataHandler
#ifndef DATAHANDLER_H
#define DATAHANDLER_H
#include <string>
#include <vector>
#include <iostream>
#include <fstream>
#include <set>
#include "constants.h"
template <typename T>
using Car = std::pair< T, T>;
template <typename T>
using SparseMatrix = std::vector< Car<T> >;
template <class T>
class DataHandler
{
public:
// initializes a new DataHandler only if none has been created,
// otherwise return the living instance
static DataHandler<T>* getInstance()
{
if(!dataHandler)
dataHandler = new DataHandler();
return dataHandler;
}
void readFile();
SparseMatrix<T>* getSparseBlue(){ return &sparseBlue; }
SparseMatrix<T>* getSparseRed(){ return &sparseRed; }
virtual ~DataHandler();
private:
// static DataHandler to ensure only one instance can be created
static DataHandler<T> *dataHandler;
// private constructor to use DataHandler as a Singleton
DataHandler();
int numElem = 0;
int m_rows, m_cols = -1;
#endif // DATAHANDLER_H
The source file is:
#include "data_handler.h"
#include <fstream>
#include <algorithm>
#include <omp.h>
#include <chrono>
using namespace std;
using namespace constants;
// Global static pointer used to ensure a single instance of the class.
template<typename T>
DataHandler<T>* DataHandler<T>::dataHandler = NULL;
template<typename T>
DataHandler<T>::DataHandler()
{
//ctor
}
template<typename T>
DataHandler<T>::~DataHandler()
{
//dtor
}
template<typename T>
void DataHandler<T>::readFile()
{
// do some stuff
}
// Instantiation of relevant templates
template class DataHandler<unsigned char>;
template class DataHandler<unsigned short int>;
In the last two lines I instantiate the templates which I define in main.cpp:
#include <iostream>
#include <chrono>
#include <fstream>
#include <algorithm>
#include "data_handler.h"
#include "dense_traffic_handler.h"
#include "sparse_traffic_handler.h"
#include "constants.h"
using namespace std;
// Check the number of rows/cols to choose between char or short int for the sparse case
bool matrixIsSmall()
{
return true;
}
void integerCase()
{
typedef unsigned char T;
DataHandler<T> *dh = DataHandler<T>::getInstance();
dh->readFile();
DenseTrafficHandler dth(dh); // ****** ERROR HERE *****
}
void charCase()
{
typedef unsigned char T;
DataHandler<T> *dh = DataHandler<T>::getInstance();
dh->readFile();
DenseTrafficHandler dth(dh); // ****** ERROR HERE *****
SparseTrafficHandler<T> sth;
set<unsigned short int> step = dh->getstep();
int currentStep = 0;
set<unsigned short int>::const_iterator stepToSave = step.begin();
}
int main(int argc, char *argv[])
{
if(matrixIsSmall())
charCase();
else
integerCase();
return 0;
}
Compiler gives me an error: undefined reference to DenseTrafficHandler::DenseTrafficHandler<unsigned short>(DataHandler<unsigned short>*)
DenseTrafficHandler header is like that:
#ifndef TRAFFICHANDLER_H
#define TRAFFICHANDLER_H
#include "constants.h"
#include "data_handler.h"
class DenseTrafficHandler
{
public:
template<typename T>
DenseTrafficHandler(DataHandler<T> *dh);
virtual ~DenseTrafficHandler();
private:
int m_cols, m_rows;
char* data;
char ** dense = NULL;
};
#endif // TRAFFICHANDLER_H
DenseTrafficHandler source is:
#include "dense_traffic_handler.h"
using namespace std;
using namespace constants;
template <typename T>
DenseTrafficHandler::DenseTrafficHandler(DataHandler<T> *datah)
{
DataHandler<T> *dh = datah;
dense = dh->getDense();
m_rows = dh->getm_rows();
m_cols = dh->getm_cols();
}
DenseTrafficHandler::~DenseTrafficHandler()
{
//dtor
}
So I have two questions:
Why do I receive this error and how can I manage it?
Is there a way in DataHandler source to not specify
template <typename T>
DataHandler<T>::functionName() for every function? (I mean something like using namespace Datahandler<T>)
You receive this error because compiler did not generate the code for this template type. One of solutions is to tell the compiler to do this explicitly by template instantiation:
add to your DenseTrafficHandler.cpp:
template class DenseTrafficHandler<unsigned short>;
Yes, just implement it in the header file. Reading more about it here.
I am trying to create a class linkedList using template but when I compile it the IDE gives an error :
undefined reference to `listType::add(int)
I am not understanding why ?
linkedList.h
#ifndef LINKEDLISTS_H_INCLUDED
#define LINKEDLISTS_H_INCLUDED
#include "struct.h"
template <class type1>
class listType
{
public:
void add(type1);
void print();
private:
node<type1> *head;
};
#endif // LINKEDLISTS_H_INCLUDED
LinkedList.cpp
#include "linkedLists.h"
#include "struct.h"
#include <iostream>
using namespace std;
template <class type1>
void listType<type1>::add(type1 temp)
{
node<type1> *t;
t->value=temp;
t->link=head;
head=t;
}
template <class type1>
void listType<type1>::print()
{
node<type1> *p;
p=head;
while(p!=NULL)
{
cout<<p->value<<endl;
p=p->link;
}
}
Struct.h
#ifndef STRUCT_H_INCLUDED
#define STRUCT_H_INCLUDED
template <class type1>
struct node
{
type1 value;
node *link;
};
#endif // STRUCT_H_INCLUDED
main.cpp
#include <iostream>
#include "linkedLists.h"
using namespace std;
int main()
{
listType <int> test;
test.add(5);
}
You can't have the implementation of templated classes and functions in the cpp file.
The code has to be in the header, so the including files can see the implementation, and instantiate the correct version with their template argument type.
I'm trying to create a linked list class in Eclipse but I can't get it to compile properly.
Here is my .cc file (code snipet)
#include <iostream>
#include "list.h"
using namespace std;
template <class T>
bool List<T>::isEmpty()
{
return (firstNode == NULL);
}
and here is my list.h file (code snipet)
#ifndef __LIST_H__
#define __LIST_H__
template <typename T>
class List {
public:
bool isEmpty();
private:
struct node {
node *following;
node *previous;
T *contents;
};
node *firstNode;
};
#include "list.cc"
#endif /* __LIST_H__ */
I try "Building All" in eclipse but I get the following error:
make all
Building file: ../list.cc
Invoking: Cross G++ Compiler
g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"list.d" -MT"list.d" -o "list.o" "../list.cc"
../list.cc:13: error: redefinition of 'bool List<T>::isEmpty()'
../list.cc:13: error: 'bool List<T>::isEmpty()' previously declared here
make: *** [list.o] Error 1
Help please...thanks. I'll be happy to provide any clarifications needed
EDIT: I was given the .h file so I know that it is correct. I also know that I am supposed to have a .cc file called list.cc (it is included at the end of the .h file)
You need to change the extension of the file with the implementation.
The compiler will process this file for compilation and will process it twice, since you're including it in the header.
Your file looks like this:
#include <iostream>
#include "list.h"
using namespace std;
template <class T>
bool List<T>::isEmpty()
{
return (firstNode == NULL);
}
which will become
#include <iostream>
#ifndef __DLIST_H__
#define __DLIST_H__
template <typename T>
class List {
public:
bool isEmpty();
private:
struct node {
node *following;
node *previous;
T *contents;
};
node *firstNode;
};
#include "dlist.cc"
#endif /* __DLIST_H__ */
using namespace std;
template <class T>
bool List<T>::isEmpty()
{
return (firstNode == NULL);
}
which will in turn become
#include <iostream>
#ifndef __DLIST_H__
#define __DLIST_H__
template <typename T>
class List {
public:
bool isEmpty();
private:
struct node {
node *following;
node *previous;
T *contents;
};
node *firstNode;
};
template <class T>
bool List<T>::isEmpty()
{
return (firstNode == NULL);
}
#endif /* __DLIST_H__ */
using namespace std;
template <class T>
bool List<T>::isEmpty()
{
return (firstNode == NULL);
}
So the function isEmpty() is defined twice.
Rename the file to dlist.impl.
Try putting the definition for List<T>::isEmpty() in the same file as the class is declared.
Given the unusual form of the header you've been supplied with, to test it you will need another source file. To start with the new source file (say test.cpp) can just #include "list.h", which will check for any syntax errors but will not yet instantiate your List template.
(Just compile test.cpp, not list.cc, since list.cc is indirectly included by test.cpp)