This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 9 years ago.
I'm working on own double linked list and everytime after adding object of class DoubleList in Evidence.cpp I get a LNK2019 error: Unresolved external symbol. I will be glad for every advice. Here are my codes:
StudentRecord.h
#pragma once
#include <string>
#include <iostream>
#include <algorithm>
#include "Student.h"
#include "DoubleList.h"
using namespace std;
using namespace SemestralWork;
class StudentRecord{
public:
DoubleList<Student> *List; //declared object (in StudentRecord.cpp is problem with that)
StudentRecord(void);
~StudentRecord(void);
Student &SearchStudent(const string &ID);
void addStudent(const Student &student, Student::Position position = Student::Position::LAST);
Student RemoveStudent(const string &ID);
void WriteAllStudents(void);
void Cancel(void);
};
StudentRecord.cpp (just part)
#include "StdAfx.h"
#include "StudentRecord.h"
using namespace SemestralWork;
StudentRecord::StudentRecord(void)
{
List = new DoubleList<Student>(); // <---- here is first LNK2019 error
}
Student &StudentRecord::SearchStudent(const string &ID){
Student * SearchedStudent;
Student * EmptyStudent = NULL;
//********** down here are next 4 LNK2019 errors. ************
for(DoubleList<Student>::iterator it = List->begin(); it != List->end(); ++it){
if(ID == List->AccessActual().getID()){
SearchedStudent = &List->AccessActual();
return *SearchedStudent;
}
} // 5 unresolved externals
return *EmptyStudent;
}
//...
DoubleList (just constructor)
template<typename T>
DoubleList<T>::DoubleList(void){
NumberOfElements = 0;
First= NULL;
Last= NULL;
Actual= NULL;
}
Student.h
#pragma once
#include <string>
using namespace std;
class Student
{
private:
string firstName, lastName, ID;
public:
Student(string, string, string);
~Student(void);
string getFirstName();
string getLastName();
string getID();
enum Position{ FIRST, LAST, ACTUAL, PREVIOUS, NEXT};
};
EDIT: Error message here:
Error 5 error LNK2019: unresolved external symbol "public: class Student & __thiscall SemestralWork::DoubleList::AccessActual(void)" (?AccessActual#?$DoubleList#VStudent###SemestralWork##QAEAAVStudent##XZ) referenced in function "public: class Student & __thiscall StudentRecord::SearchStudent(class std::basic_string,class std::allocator > const &)" (?SearchStudent#StudentRecord##QAEAAVStudent##ABV?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std###Z)
(one of five LNK errors)
So, you have a message. I'll break the message in several lines. The message should be read like this:
LNK2019: unresolved external symbol
"some function or variable that compiler saw nicely declared but the linker can't find the definition of"
(name of the missing symbol as linker sees it)
referenced in function
"some function where the missing function/variable is being used"
(name of the function as linker sees it)
In your case linker needs function DoubleList::AccessActual(void) in namespace SemestralWork. The function is declared somewhere, most likely in DoubleList.h. You probably need to add DoubleList.cpp file to the project. Maybe you forgot to define the function? In that case you have to write it.
Also, you really, really need to remove using namespace lines from header files. Really! Classes that exist in namespaces MUST be declared like this:
namespace SomeNamespace {
class SomeClass
{
void SomeFunction();
...
}
}
And SHOULD be defined like this in source file:
void SomeNamespace::SomeClass::SomeFunction()
{
...
}
In header files all stuff from any other namespaces, including std namespace, SHOULD be used with full name (std::string). In source files you MAY use using namespace std AFTER all #include directives. Some people disagree on this last one, but it's a matter of style.
Related
all
i created a static lib project with VS 2010 sp1, and simply defined a class with a member function (code snippet):
.h:
namespace puphttp{
class CRequester
{
public:
void RequesterUpdate();
};
}
.cpp:
#include "StdAfx.h"
#include "Requester.h"
#include <iostream>
using namespace std;
namespace puphttp{
void CRequester::RequesterUpdate()
{
cout<<"updating";
}
}
at last i linked the lib file and tried to invoke the following code:
puphttp::CRequester c;
c.RequestUpdate();
the following link error occur as i compile:
error LNK2001: unresolved external symbol "public: void __cdecl puphttp::CRequester::RequestUpdate(void)" (?RequestUpdate#CRequest#puphttp##QEAAXXZ)
then i used dumpbin to check the actual function name in my lib, it's:
(?RequestUpdate#CRequest#puphttp##QAEXXZ)
so the difference is QEAAXXZ vs QAEXXZ, i didn't have time to get into name mangling rule yet, so any quick answer? really much appreciated.
First, this is hw and I'm supposed to change only one function. But I'm not here for help on that function, I'm here for an LNK error.
Here's the relevant output on the Developer Command Prompt after I type in cl shortest.cpp (with spaces between errors for easier reading):
shortest.obj : error LNK2019: unresolved external symbol "public: void __thiscall Graph::readFile(char *)" (?readFile#Graph##QAEXPAD#Z) referenced in function _main
shortest.obj : error LNK2019: unresolved external symbol "public: void __thiscall Graph::dijkstra(int)" (?dijkstra#Graph##QAEXH#Z) referenced in function _main
shortest.obj : error LNK2019: unresolved external symbol "public: void __thiscall Graph::printPath(int)" (?printPath#Graph##QAEXH#Z) referenced in function _main
shortest.exe : fatal error LNK1120: 3 unresolved externals
I understand this is supposed to mean I haven't defined those symbols, but they should have been predefined for me in one of two files: graph.cpp or graph.h. Graph.h seems more likely, as it contains the declarations of each of these "unresolved" symbols.
graph.h:
#include <iostream>
#include <fstream>
#include <vector>
#include <limits.h>
#include <cstdlib>
#define INFINITY INT_MAX
using namespace std;
class Graph
{
struct Edge
{
int dest; // destination vertex number
int cost; // edge weight
Edge *next;
};
struct Vertex
{
Edge *adj;
bool known;
int dist;
int path;
};
vector<Vertex *> vertices;
vector<int> PQ;
int PQsize;
void PQinsert (int v);
int PQdeleteMin ();
public:
Graph () { PQsize=0; }
int numVertices () { return vertices.size(); }
int dist (int dest) { return vertices[dest]->dist; }
void readFile (char *name);
void dijkstra (int start);
void printPath (int dest);
};
I won't post graph.cpp or shortest.cpp (which only contains the main), unless requested, as it doesn't seem to me that the content of the related functions is an issue. If I do, I will only post the related methods to keep it shorter. But graph.cpp, graph.h, and shortest.cpp are all in the same folder. And shortest.cpp does include graph.h. I'm only supposed to change the dijkstra method, but if I can add something that will make this compile without changing way the methods or class themselves work (which it shouldn't have to) I don't see a problem.
You have to use make file to build with all the source files. Otherwise you can first compile the sources and then link manually. Search google for individual commands for compiling/linking.
This question already has answers here:
Why can templates only be implemented in the header file?
(17 answers)
Closed 8 years ago.
Right I am getting weird linker errors which I've never seen before and which I can't really decipher.
Code for the RelationOwner and RelationUser can be found there. One remark: I've moved all function bodies to the source file instead of the header file. Naming has stayed the same.
Error 1 error LNK2019: unresolved external symbol "public: __thiscall RelationUser<class Family,class Citizen>::RelationUser<class Family,class Citizen>(class Family *)" (??0?$RelationUser#VFamily##VCitizen####QAE#PAVFamily###Z) referenced in function "public: __thiscall Citizen::Citizen(class Family &,class Name)" (??0Citizen##QAE#AAVFamily##VName###Z) *path*\Citizen.obj CodeAITesting
Error 2 error LNK2019: unresolved external symbol "public: __thiscall RelationUser<class Family,class Citizen>::~RelationUser<class Family,class Citizen>(void)" (??1?$RelationUser#VFamily##VCitizen####QAE#XZ) referenced in function __unwindfunclet$??0Citizen##QAE#AAVFamily##VName###Z$1 *path*\Citizen.obj CodeAITesting
Error 3 error LNK2019: unresolved external symbol "public: __thiscall RelationOwner<class Family,class Citizen>::~RelationOwner<class Family,class Citizen>(void)" (??1?$RelationOwner#VFamily##VCitizen####QAE#XZ) referenced in function __unwindfunclet$??0Family##QAE#VName###Z$1 *path*\Family.obj CodeAITesting
The first one is about a constructor and the second two are about the destructor. That I understand.
I've also implemented my own version of the User and Owner as the following:
// header of Family.h (Owner in the linked PDF file)
#include "Name.h"
#include "RelationOwner.h"
class Citizen;
class Family; // I didn't really know if this one was necessary.
class Family
: public RelationOwner<Family, Citizen>
{
public:
Family(Name name);
private:
Name name;
};
// Source of Family.cpp
#include "Name.h"
Family::Family(Name name)
: name(name)
{
}
//Source of Citizen.h (User in the linked PDF)
#include "Name.h"
#include "RelationUser.h"
class Citizen;
class Family;
class Citizen
: public RelationUser<Family, Citizen>
{
public:
Citizen(Family &family, Name name);
private:
Name name;
};
// Source of Citizen.cpp
#include "Family.h"
#include "Name.h"
#include "RelationUser.h"
Citizen::Citizen(Family &family, Name name)
: RelationUser<Family, Citizen>(&family),
name(name)
{
}
As far as I know I am not doing anything fancypancy, yet it is complaining big time and I don't know why.
Well as Brian Beuning told me "usually the code for a template is in the header file".
And after reading n.m.'s linked possible duplicate I moved the implementation back to the header file and, it worked.
I guess that the duplicate question was spot on.
I am trying to run a main.cpp which access 3 different classes. For some reason, I am getting a unresolved external symbol error. From what I've seen online, its clearly a linking error somewhere, but I cannot find it. I've listed the error below, but it's got a lot of info in it and im having trouble finding out exactly what it means.
The error: main.obj:-1: error: LNK2001: unresolved external symbol "public: __thiscall AtpReader::AtpReader(class std::basic_string,class std::allocator >)" (??0AtpReader##QAE#V?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std###Z)
My code is:
main.cpp:
#include <iostream>
#include "atlasobject.h"
#include "atp.h"
#include "atpreader.h"
using namespace std;
int main()
{
AtpReader reader("E:/doc.txt");
return 0;
}
AtpReader.h:
#ifndef ATPREADER_H
#define ATPREADER_H
#include "atp.h"
class AtpReader
{
public:
AtpReader();
AtpReader(string filename);
void atpReadHeader();
void atpRead();
string decryptLine(string line);
ATP readerATP;
private:
string file;
};
#endif // ATPREADER_H
atp.h:
#ifndef ATP_H
#define ATP_H
#include "atlasobject.h"
#include "vector"
struct Image{
string Dim;
string Vox;
string Ori;
char* data;
};
class ATP
{
public:
ATP();
vector<AtlasObject> listOfMaps;
private:
Image referenceImage;
};
#endif // ATP_H
and AtlasObject.h:
#ifndef ATLASOBJECT_H
#define ATLASOBJECT_H
#include <string>
using namespace std;
class AtlasObject{
public:
//virtual void create();
AtlasObject();
void set_uid(string id);
void set_label(string l);
void set_offset(string o);
void set_mapInfo(string info);
void set_data(char* inData);
void set_isEncrypted(int encrypted);
string get_uid();
string get_label();
string get_offset();
string get_mapInfo();
char* get_data();
int get_isEncrypted();
protected:
string uid;
string label;
string offset;
string mapInfo;
char *data;
int isEncrypted;
};
#endif // ATLASOBJECT_H
my AtpReader.cpp is:
#include "atpreader.h"
#include <iostream>
#include <fstream>
#include <stdint.h>
#include <sstream>
AtpReader::AtpReader()
{
printf("AtpReader()\n");
}
AtpReader::AtpReader(string filename)
{
printf("AtpReader(%s)\n",filename.c_str());
}
I see you did not include AtpReader.h in AtpReader.cpp, but probably you just missed it when you made copy/paste, to insert it here, because if you didn't really include it, the error would have been different. Also, I see you're including in your main.cpp both "atlasobject.h"
and "atp.h" and you don't really need that.
Later edit: Your problem is in the atp.h...you constructor is declared but never defined. Do this: ATP(){};
Try using g++ in linux terminal
make the object files of each of the source codes and then link the object files and run the executable
g++ -c atp.cpp AtpReader.cpp AtlasObject.cpp
g++ -o exe atp.o AtpReader.o AtlasObject.o
./exe
AtpReader.cpp is not getting built or the its object file is not getting linked to final executable. Check if AtpReader.obj/.o is created in build directory.
Because of the linker error you are getting and assuming that this is some of your actual code. Since I can't see any function inlining, global constants or variables being used out of scope I think the problem is located in the AtpReader.cpp, are you missing an #include AtpReader.h there?
With just a function prototype, the compiler can continue without error, but the linker cannot resolve a call to an address because there is no function code or variable space reserved. You will not see this error until you create a call to the function that the linker must resolve.
Hi i'm getting the following errors:
Error 9 error LNK1120: 2 unresolved externals
Error 8 error LNK2019: unresolved external symbol "public: virtual __thiscall physics::~physics(void)" (??1physics##UAE#XZ) referenced in function "public: virtual void * __thiscall physics::`scalar deleting destructor'(unsigned int)" (??_Gphysics##UAEPAXI#Z)
Error 7 error LNK2019: unresolved external symbol "public: virtual __thiscall student::~student(void)" (??1student##UAE#XZ) referenced in function __unwindfunclet$??0physics##QAE#XZ$0
which occur using the following code:
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class student{
protected:
string fName,sName;
int id;
vector<string> cname;
vector<int> cmark;
public:
virtual ~student();
virtual void addCourse(string name, int mark)=0;
};
class physics : public student{
public:
physics(){//Initialize default values
fName="blank";
sName="blank";
id=0;
cname.push_back("none");
cmark.push_back(0);
};
~physics();
void addCourse(string name, int mark){
if(cname.size()==1){//override default value for a size of 1
cname[0]=name;
cmark[0]=mark;
}
else{
cname.push_back(name);
cmark.push_back(mark);
}
}
};
The above compiles fine but when i try to initialize an object in main() by using:
int main(){
//Database Storage
vector<student*> DB;
DB.push_back(new physics);
}
That's when i get the errors (removing the push_back line fixes it but i need this for my program). What am i doing wrong?
Turns out adding braces to the end of the destructors fixed it. What difference does that make? (from the comments)
The difference is that in one case you have a declaration which lacks a definition; in the second case you provide a (empty) definition inline.
Trying to invoke a function that is declared but not defined (as in the first case) result in an unresolved reference error raised by the linker - after all, what should it do when a function invocation is found for a function whose implementation is not available?