C++ - initializing static vector of pointers causes undefined reference - c++

Question

I'm trying to create a function below in my CreateReport class called load() that copies all the records (data) from my graduate.dat file into my static vector of Record pointers called primaryCollection. I created a Record class with variables that make up each Record, and in my load() function in createReport.cc I attempted to read each line in the file, create a Record object with each line, add it to my vector, and then print everything in primaryCollection.
The problem is every time I attempt to use primaryCollection, I keep getting the error:
CreateReport.o: In function `CreateReport::CreateReport()':
CreateReport.cc:(.text+0x43): undefined reference to `CreateReport::primaryCollection'
CreateReport.o: In function `CreateReport::load()':
CreateReport.cc:(.text+0x2ac): undefined reference to `CreateReport::primaryCollection'
CreateReport.cc:(.text+0x31d): undefined reference to `CreateReport::primaryCollection'
CreateReport.cc:(.text+0x32f): undefined reference to `CreateReport::primaryCollection'
I get 4 undefined references for the 4 times I mention primaryCollection in createReport.cc. I'm not sure if I'm initializing primaryCollection correctly and if that is whats causing these undefined references. I don't know if this is relevant to my problem, but CreateReport is also an abstract class and has a few subclasses called ReportOne, ReportTwo, etc.
primaryCollection is supposed to be a static vector of Record pointers and I'm also not allowed to use std::map for this task.
I would appreciate any help with this issue. I looked at this post Undefined reference to static variable c++ but I still don't really understand what to do. I'm not allowed to make global variables and I'm dealing with a collection rather than a single variable.
My graduate.dat file is formatted like below in the format < year province degree >
2000 AB Bachelor's
2005 AB Bachelor's
2005 MB College
Each line basically represents a Record. So the first record here is 2000 AB Bachelor's
EDIT: So I made changes to my code based on the comments by adding the line vector<Record*> CreateReport::primaryCollection; above my constructor, but it gives me the error:
CreateReport.cc:13:34: error: conflicting declaration ‘std::vector<Record*> CreateReport::primaryCollection’
vector<Record*> CreateReport::primaryCollection;
^~~~~~~~~~~~~~~~~
In file included from CreateReport.cc:5:0:
CreateReport.h:23:33: note: previous declaration as ‘std::vector<Record*>* CreateReport::primaryCollection’
static std::vector<Record*>* primaryCollection; //STL vector of record pointers
^~~~~~~~~~~~~~~~~
CreateReport.cc:13:34: error: declaration of ‘std::vector<Record*>* CreateReport::primaryCollection’ outside of class is not definition [-fpermissive]
vector<Record*> CreateReport::primaryCollection;
Any ideas how to fix this?
Record.h
#ifndef RECORD_H
#define RECORD_H
#include <iostream>
#include <string>
class Record{
public:
Record(int = 0, string = "", string = "");
~Record();
private:
int year;
string province;
string degree;
};
#endif
Record.cc
#include <iostream>
#include <string>
using namespace std;
#include "Record.h"
Record::Record(int i1, string s1, string s2) : year(i1), province(s1), degree(s2){}
Record::~Record(){}
CreateReport.h
#ifndef CREATEREPORT_H
#define CREATEREPORT_H
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <iterator>
#include <algorithm>
#include <cstdlib>
#include "Record.h"
class CreateReport{
public:
CreateReport();
static void load();
protected:
static vector<Record*> primaryCollection; //STL vector of record pointers
};
#endif
CreateReport.cc
#include <iostream>
using namespace std;
#include <string>
#include "CreateReport.h"
vector<Record*> CreateReport::primaryCollection;
CreateReport::CreateReport(){
}
void CreateReport::load(){
int year;
string province, degree;
ostream_iterator<Record*> outItr(cout);
ifstream infile("graduate.dat", ios::in);
if (!infile) {
cout << "Error: could not open file" << endl;
exit(1);
}
while (infile >> year >> province >> degree) { //as long as were not at end of file
Record* record = new Record(year, province, degree); //create Record object with this data
primaryCollection->push_back(record); //undefined reference
}
cout<<endl<<"List of Records:"<<endl;
copy(primaryCollection->begin(), primaryCollection->end(), outItr); //2 undefined references
}

Answer 1

Second version using `Record*` for `std::vector primaryCollection`.
#include <iostream>
#include <string>
#include <fstream>
#include <vector>
using namespace std;
class Record{
public:
Record(int = 0, string = "", string = "");
~Record()=default;
friend std::ostream& operator<<(std::ostream&, const Record&);
private:
int year;
string province;
string degree;
};
// **** output overload for Record ***********
std::ostream& operator<<(std::ostream& os, const Record& rd)
{
os << "year = " << rd.year << " prov = " << rd.province << " degree = " << rd.degree << std::endl;
return os;
}
// ****** end of output overload **************
Record::Record(int i1, string s1, string s2) : year(i1), province(s1), degree(s2){}
//end of Record.cc
//
class CreateReport{
public:
CreateReport() = default;
void load();
protected:
static vector<Record*> primaryCollection; //STL vector of record pointers
};
//***************** you need this line ********************
std::vector<Record*> CreateReport::primaryCollection;
//*********************************************************
void CreateReport::load(){
int year;
string province, degree;
ifstream infile("graduate.dat", ios::in);
if (!infile) {
cout << "Error: could not open file" << endl;
exit(1);
}
while (infile >> year >> province >> degree) {
Record *a = new Record(year, province, degree);
primaryCollection.push_back( a );
}
cout<<endl<<"List of Records:"<<endl;
for (int i = 0; i<primaryCollection.size(); ++i ) std::cout << *primaryCollection[i];
}
int main()
{
CreateReport mime;
mime.load();
}

Answer 2

Three major problems:
Using std::vector<*Record> cause many un-necessary difficulties;
For static member vector, a extra definition outside the class is necessary.std::vector<Record> CreateReport::primaryCollection;. This erases the undefined error message.
Using copy to std::cout doesn't work, it provide no method of printing Record. Suggest to write a output overload.
Based on these, I provide a version as follows (mixed all headers together.)
#include <iostream>
#include <string>
#include <fstream>
#include <vector>
using namespace std;
class Record{
public:
Record(int = 0, string = "", string = "");
~Record()=default;
friend std::ostream& operator<<(std::ostream&, const Record&);
private:
int year;
string province;
string degree;
};
// **** output overload for Record ***********
std::ostream& operator<<(std::ostream& os, const Record& rd)
{
os << "year = " << rd.year << " prov = " << rd.province << " degree = " << rd.degree << std::endl;
return os;
}
// ****** end of output overload **************
Record::Record(int i1, string s1, string s2) : year(i1), province(s1), degree(s2){}
//end of Record.cc
//
class CreateReport{
public:
CreateReport() = default;
void load();
protected:
static vector<Record> primaryCollection;
};
//***************** you need this line ********************
vector<Record> CreateReport::primaryCollection;
//*********************************************************
void CreateReport::load(){
int year;
string province, degree;
ifstream infile("graduate.dat", ios::in);
if (!infile) {
cout << "Error: could not open file" << endl;
exit(1);
}
while (infile >> year >> province >> degree) {
primaryCollection.push_back( Record(year, province, degree) );
}
cout<<endl<<"List of Records:"<<endl;
for (int i = 0; i<primaryCollection.size(); ++i ) std::cout << primaryCollection[i];
}
int main()
{
CreateReport mime;
mime.load();
}