Have the following program:
#include <iostream>
#include <string>
using namespace std;
class Record
{
public:
static Record* GetInstance(string name);
void printName();
private:
Record(string name);
string name_;
static Record *record;
};
Record::Record(string name)
:name_(name)
{
}
Record*
Record::GetInstance(string name)
{
if(record == NULL) {
record = new Record(name);
}
return record;
}
void
Record::printName()
{
cout << name_ << endl;
}
int main()
{
Record* record1 = Record::GetInstance("sellers");
record1->printName();
Record* record2 = Record::GetInstance("customers");
record2->printName();
}
I am compiling and linking with:
g++ -g -c -Wall main.cpp
g++ -g -Wall main.o -o main
The compilation completes without error(1st command). But the linking is giving this error:
Undefined first referenced
symbol in file
Record::record main.o
ld: fatal: Symbol referencing errors. No output written to main
collect2: ld returned 1 exit status
Wondering how to correct this.
You need to define the variable somewhere, i.e.
Record *Record::record;
Related
I am getting the error shown below while linking the code. How can I fix this problem?
It seems the static variable is not getting initialized.
#include <iostream>
#include <cstdlib>
using namespace std;
struct name{
char c;
};
class List {
static name *a;
public:
static void modify()
{
a = new name();
cout<<"yes";
}
};
name List::*a = NULL;
int main()
{
List::modify();
}
g++ O3 -Wall -c -fmessage-length=0 -o sample.o "..\\sample.cpp"
g++ -o sample.exe sample.o
sample.o:sample.cpp:(.text.startup+0x35): undefined reference to `List::a'
collect2.exe: error: ld returned 1 exit status
name List::*a = NULL; doesn't do what you expected. It defines a global variable named a, which is a pointer to non-static member of List of type name.
The definition of List::a should be
name* List::a = NULL;
I am writing a simple server program using ICE by ZeroC. When I try to link the .o files it gave me the following error message:
$ c++ -o server UserMap.o Server.o -L/Library/Developer/Ice-3.5.0/lib -lIce -lIceUtil
Undefined symbols for architecture x86_64:
"VTT for UserMapI", referenced from:
UserMapI::UserMapI() in Server.o
"vtable for UserMapI", referenced from:
UserMapI::UserMapI() in Server.o
NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
After some googling I understand that the problem is I have an abstract class with 3 virtual methods declared in UserMap.ice (and hence in UserMap.h and UserMap.cpp generated by the command slice2cpp UserMap.ice), and in Server.cpp I have a class called UserMapI:public UserMap which implements the three virtual methods and another private helper function. The error is generated because the compiler thinks I have declared all functions(methods) in UserMap.h and UserMap.cpp.
My understanding to this problem is that I should modify the link command so that the linker will know that there are more functions in UserMapI declared in Server.cpp, but I don't have enough knowledge to do the modification. Can someone help me please?
Thank you all.
Here is the compiler command I am using to get Server.o and UserMap.o:
c++ -I. -I/Library/Developer/Ice-3.5.0/include -c UserMap.cpp Server.cpp
Here's the code of UserMap.ice:
module DR
{
class UserMap
{
void addUserToLocation(int userID, int x, int y);
string getUsersNearLocation(int x, int y, int distance);
void removeFromMap(int userID, int x, int y);
};
};
slice2cpp command slices this .ice file into a .h and a .cpp file that works as an API between server and client.
In Server.cpp I have the following include:
#include <Ice/Ice.h>
#include "UserMap.h"
#include <map>
#include <string>
#include <vector>
#include <iostream>
#include <sstream>
and the following subclass:
class UserMapI : public UserMap
{
public:
virtual void addUserToLocation(int userID, int x, int y, const Ice::Current &);
virtual string getUsersNearLocation(int x, int y, int distance, const Ice::Current &);
virtual void removeFromMap(int userID, int x, int y, const Ice::Current &);
private:
string stringify(int x, int y);
};
And after implementing all methods here's the main function:
int main(int argc, char* argv[])
{
int status = 0;
Ice::CommunicatorPtr ic;
try {
ic = Ice::initialize(argc, argv);
Ice::ObjectAdapterPtr adapter = ic->createObjectAdapterWithEndpoints("SimpleUserMapAdapter", "default -p 10000");
Ice::ObjectPtr object = new UserMapI;
adapter->add(object, ic->stringToIdentity("SimpleUserMap"));
adapter->activate();
ic->waitForShutdown();
} catch (const Ice::Exception & e) {
cerr << e << endl;
status = 1;
} catch (const char * msg) {
cerr << msg << endl;
status = 1;
}
if (ic){
try {
ic->destroy();
} catch (const Ice::Exception & e) {
cerr << e << endl;
status = 1;
}
}
return status;
}
Here's the UserMap.h.
I wrote a class named UserScore:
//header
using namespace std;
class UserScore{
public:
UserScore(const int &user_id, const int &rating);
private:
int _user_id;
int _rating;
};
//cpp
#include "UserScore.h"
UserScore::UserScore (const int &user_id, const int &rating):
_user_id(user_id),
_rating(rating)
{
}
The compile command is:
g++ src/UserScore.cpp -o obj/UserScore.o
But why this simple thing won't compile?
The error is:
Undefined symbols for architecture x86_64:
"_main", referenced from:
start in crt1.10.6.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
You need to include the -c option to the compilation line if you want to generate an object file, otherwise the compiler assumes you are trying to build an executable and will complain if you don't have a main() method (which is happening here).
To make an object file which you will link later to a code file that has a "main()" method in it you need to use
g++ -c src/UserScore.cpp -o obj/UserScore.o
Which is what I think you are trying to do.
Alternatively you just need to add a main function to your code and then you can make an executable.
//header
using namespace std;
class UserScore{
public:
UserScore(const int &user_id, const int &rating);
private:
int _user_id;
int _rating;
};
//cpp
#include "UserScore.h"
UserScore::UserScore (const int &user_id, const int &rating):
_user_id(user_id),
_rating(rating)
{
}
int main()
{
return 0;
}
This is the error I am keep getting . undefined reference to my class. I am not sure. I think I m linking them. this is how my main looks like.
#include <iostream>
#include "randomNumberMagnifier.h"
using namespace std;
int main()
{
randomNumberMagnifier r1, r2;
cout << "Random Number "<< r1.getRandomNumber();
cout << endl;
}
I am not sure what I am doing wrong.
this is what it looks like. when I compile
[singha1#cs1 p4]$ g++ -c randomNumberMagnifier.cpp
[singha1#cs1 p4]$ g++ -o p4Driver.cpp
g++: no input files
p4Driver.cpp:(.text+0x8c): undefined reference to `randomNumberMagnifier::getRandomNumber
collect2: ld returned 1 exit status
#ifndef RANDOMNUMBERMAGNIFIER_H
#define RANDOMNUMBERMAGNIFIER_H
class randomNumberMagnifier
{
int addFactor;
int multFactor;
bool addOn;
bool multOn;
int randomNumber;
static const int MAX_ADD_FACTOR = 100;
static const int MAX_MULT_FACTOR = 20;
static const int MAX_RANDOM = 200;
public:
randomNumberMagnifier();
//~randomNumberMagnifer();
randomNumberMagnifier& operator=(const randomNumberMagnifier& rhs);
randomNumberMagnifier(const randomNumberMagnifier& arandom);
randomNumberMagnifier(bool aState, bool mState);
int randomMagnifier();
int getAdd();
int getMult();
bool getAddState();
bool getMultState();
int getRandomNumber();
};
#endif
g++ -o p4Driver.cpp
That doesn't say what it's supposed to compile to, which is what -o is supposed to be for. You want:
g++ -c randomNumberMagnifier.cpp
g++ -c p4Driver.cpp
g++ randomNumberMagnifier.o p4Driver.o -o p4Driver
Or just:
g++ randomNumberMangifier.cpp p4Driver.cpp -o p4Driver
you need to provide randomNumberMagnifier.o to g++ command, so it can find function definition. I tested with below command and i worked
g++ -o p4Driver p4Driver.cpp randomNumberMagnifier.o
Looked around and found a few similar questions but none of them were the same. Most had to do with the constructor or destructor. This issue is, more than likely, a result of my rusty C++ linker memory (picking it back up after a few years).
I'll keep it real simple since this is probably a basic misunderstanding of the linker:
data.h
#pragma once
namespace test {
class Data_V1 {
public:
// some getters/setters
int getData() { return _d; }
void setData( int d ) { _d = d; }
private:
// some data
int _d;
};
}
builder.h
#pragma once
namespace test {
template <class V>
class Builder {
public:
void build();
};
}
builder.cpp
#include <iostream>
#include "builder.h"
namespace test {
template<class V>
void Builder<V>::build() {
std::cout << "Insert building logic" << std::endl;
}
}
main.cpp
#include "builder.h"
#include "data.h"
using namespace test;
int main(int argc, char* argv[]) {
Builder<Data_V1> b;
b.build();
}
compiling:
g++ -Wall -ansi -pedantic -c builder.cpp
g++ -Wall -ansi -pedantic -c main.cpp
g++ -Wall -ansi -pedantic -o main main.o builder.o
Link error:
Undefined symbols for architecture x86_64:
"test::Builder<test::Data_V1>::build()", referenced from:
_main in main.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
Any help would be appreciated!
Template definitions need to be visible to all translation units. Move the definition from the cpp to the header.
Builder.h
#pragma once
namespace test {
template <class V>
class Builder {
public:
void build();
};
template<class V>
void Builder<V>::build() {
std::cout << "Insert building logic" << std::endl;
}
}
Before you ask, no, there's no way to hide the implementation unless you know all possible specializations beforehand.
Templates represent a generalized form for the creation of a new class. If the implementation is not visible, when you attempt to specialize the template, the compiler can't know what code to generate.