This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 8 years ago.
I'm still learing c++ and was following an example from my book. I basically copied their code and added the include and namespace. What am I doing wrong?
Code:
#include <iostream>
#include <string>
using namespace std;
class Date{
int y,m,d;
public:
Date(int y, int m, int d);
int month(){return m;}
int day(){return d;}
int year(){return y;}
};
int main(){
Date b{1970,12,30};
cout<< b.month()<< '\n';
}
Trying to compile with g++ -std=c++11 -o test2 test2.cc
Error:
Date::Date(int, int, int) /var/tmp//ccGuivAs.o
ld: fatal: Symbol referencing errors. No output written to main
collect2: ld returned 1 exit status
Date(int y, int m, int d);
The error message is signaling (in an admittedly unclear way) that there's no definition for Date. It's declared, but not defined. You didn't specify what the constructor does.
Date(int y, int m, int d) {
this->y = y;
this->m = m;
this->d = d;
}
Or, better, using initializer list syntax:
Date(int y, int m, int d): y(y), m(m), d(d) { }
You have to add implementation (definition) of constructor
Date(int y, int m, int d);
At the moment there is only a declaration found in your Date class and such a situation results in
undefined reference to `Date::Date(int, int, int)' collect2: error: ld
returned 1 exit status
http://ideone.com/wMgbKX
You declared the Date::Date constructor, but never defined it.
Your declaration is a promise to the compiler that the constructor Date::Date will be defined somewhere. But you never actually provided a definition. That is what's causing the error.
You can provide a definition right there, inside the class definition, like you did with other member functions. Or you can provide a definition outside the class. It is up to you. But a definition has to be provided somewhere.
You need to implement Date::Date(int, int, int) (i.e. the Date constructor) somewhere, as explicitly stated by your compiler.
You could do that by adding a body to it, like for its month, day and year methods, or outside of the class.
Related
I am using a simple function to add to integers, the class is declared in the Adder.h file as below
class Adder
{
public:
int add (int x, int y);
};
Then I have the Adder.cpp file which has the function definition
int add (int x, int y)
{
return x + y;
}
Then the main.cpp file which calls the function
# include "Adder.h"
# include <iostream>
using namespace std;
int main()
{
Adder adder1;
int result = adder1.add (2, 3);
cout << result;
}
I ran g++ -c Adder.cpp to create Adder.o file beforehand.
Then I ran g++ main.cpp but go the following error
main.cpp:(.text+0x2d): undefined reference to `Adder::add(int, int)'
Where am I going wrong?
In your second and final step, you didn't instruct the compiler (linker more exactly) to take into account Adder.o, so your final executable still doesn't know the implementation of Adder::add
Try, after getting Adder.o, to run g++ main.cpp Adder.o
Also, this may be relevant : Difference between compiling with object and source files
Also, if that is the complete code, as others have pointed out, in the Adder.cpp, you are just defining a simple function, not the one from the Adder class.
The problem is that you've defined a free function named add instead of defining a member function of class Adder. To define add as a member function we have to be in the scope of the class Adder which we can do by adding Adder:: before add as shown below:
Adder.cpp
//note the use of scope resolution operator ::
int Adder::add(int x, int y)//define a member function instead of a free function
{
return x + y;
}
In the above modified code, we are defining the member function add instead of the free function add.
I am using a simple function to add to integers, the class is declared in the Adder.h file as below
class Adder
{
public:
int add (int x, int y);
};
Then I have the Adder.cpp file which has the function definition
int add (int x, int y)
{
return x + y;
}
Then the main.cpp file which calls the function
# include "Adder.h"
# include <iostream>
using namespace std;
int main()
{
Adder adder1;
int result = adder1.add (2, 3);
cout << result;
}
I ran g++ -c Adder.cpp to create Adder.o file beforehand.
Then I ran g++ main.cpp but go the following error
main.cpp:(.text+0x2d): undefined reference to `Adder::add(int, int)'
Where am I going wrong?
In your second and final step, you didn't instruct the compiler (linker more exactly) to take into account Adder.o, so your final executable still doesn't know the implementation of Adder::add
Try, after getting Adder.o, to run g++ main.cpp Adder.o
Also, this may be relevant : Difference between compiling with object and source files
Also, if that is the complete code, as others have pointed out, in the Adder.cpp, you are just defining a simple function, not the one from the Adder class.
The problem is that you've defined a free function named add instead of defining a member function of class Adder. To define add as a member function we have to be in the scope of the class Adder which we can do by adding Adder:: before add as shown below:
Adder.cpp
//note the use of scope resolution operator ::
int Adder::add(int x, int y)//define a member function instead of a free function
{
return x + y;
}
In the above modified code, we are defining the member function add instead of the free function add.
This question already has answers here:
Separating class code into a header and cpp file
(8 answers)
Closed 1 year ago.
Just had a little problem that I haven't been able to figure out yet.
I was using a similar program structure for a different project, but the problem boils down to this. I have two cpp files, which are:
Trading_dte.cpp :
#include <iostream>
using namespace std;
class Dte
{
public:
int addition(int a, int b)
{
return a + b;
}
};
dummy.cpp :
#include <iostream>
#include "Trading_dte.hpp"
Dte obj;
int check()
{
std::cout<<obj.addition(6,9);
}
I created a header file called Trading_dte.hpp :
# pragma once
#include <iostream>
class Dte
{
public:
int addition(int a, int b);
};
Now when I try compiling using the command :
g++ Trading_dte.cpp dummy.cpp
I get the error :
/usr/bin/ld: /tmp/ccCcM8R6.o: in function `check':
dummy.cpp:(.text+0x1a): undefined reference to `Dte::addition(int, int)'
collect2: error: ld returned 1 exit status
I'm sure it's something small, but I just can't figure what.
Thanks a lot in advance!
your cpp file need to be written differently
#include "Trading_dte.hpp"
#include <iostream>
int Dte::addition(int a, int b)
{
return a + b;
}
You've created two separate Dte classes, one visible to main and another visible only in Trading_dte.cpp. The one visible to main, defined in Trading_dte.hpp has a declaration of the addition member function but no definition.
Probably the easiest thing to do is to drop Trading_dte.cpp and put the implementation into the class definition in Trading_dte.hpp.
Trading_dte.hpp:
# pragma once
class Dte
{
public:
int addition(int a, int b)
{
return a + b;
}
};
Note that I also removed the #include <iostream> line. You don't need it in the header file because you don't use it in the class.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
What is an undefined reference/unresolved external symbol error and how do I fix it?
I recently started working on an interpreter in C++, but I got annoyed that vectors or arrays could not be passed to external class methods no matter what I tried and so I deleted everything I had worked on. As it turns out, I can't pass even an int to another class. I decided to give C++ another chance before resorting to C or Java, but the compiler still doesn't work as I would expect. Maybe I'm forgetting something simple about C++, as I haven't used it in a while, but this seems simple enough. My problem is: I can't pass arguments to methods in other classes when they're not defined in the same file. Here's what I'm trying to do:
Main: main.cpp
#include "myclass.h"
int main() {
MyClass test;
int n = test.add(25, 30);
return n;
}
Header: myclass.h
class MyClass {
public:
int add(int a, int b);
};
Class implementation: myclass.cpp
#include "myclass.h"
int MyClass::add(int a, int b) {
return a + b;
}
Compiling this with g++ main.cpp yields
/tmp/ccAZr6EY.o: In function main':
main.cpp:(.text+0x1a): undefined reference toMyClass::add(int, int)'
collect2: error: ld returned 1 exit status
What the heck am I doing wrong? Also, the compiler yells at me for the same thing even if my functions aren't parameterized, so it must be a problem with the header.
Any help is much appreciated - thanks!
You need to compile both files
g++ main.cpp myclass.cpp
If you only compile main.cpp, the compiler finds the declaration of MyClass::add in your header but the linker later fails to find an implementation of MyClass::add to jump to.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
undefined reference to static member variable
What is an undefined reference/unresolved external symbol error and how do I fix it?
#include<iostream>
using namespace std;
class abc {
private:
static int a ;
public:
abc(int x) {
a = x;
}
void showData() {
cout<<"A = "<<a<<endl;
}
};
int main() {
abc a1(4);
abc a2(5);
a1.showData();
a2.showData();
return 0;
}
When I try to compile this function on Ubuntu with GCC compiler. I get the following error.
/tmp/ccCKK2YN.o: In function `main':
static1.cpp:(.text+0xb): undefined reference to `Something::s_nValue'
static1.cpp:(.text+0x14): undefined reference to `Something::s_nValue'
collect2: ld returned 1 exit status
Compilation failed.
Where as the following code runs fine
#include<iostream>
using namespace std;
class Something
{
public:
static int s_nValue;
};
int Something::s_nValue = 1;
int main()
{
Something cFirst;
cFirst.s_nValue = 2;
Something cSecond;
std::cout << cSecond.s_nValue;
return 0;
}
Is this because Static member variables needs to initialized explicitly before accessing them via objects.Why so ?
static int s_nValue; doesn't allocate any storage to store the int, it just declares it.
You allocate somewhere in memory to store the variable with:
int Something::a=0;
The declaration of a static data member in the member list of a class is not a definition. You must define the static member outside of the class declaration, in namespace scope.
See this thread.
In short, the static member needs to be initialized somewhere in a .cpp file so that the compiler allocates space for it. The declaration would look like this:
int abc::a = 0;
That happens because since static members are shared between all instances of a class, they need to be declared in one single place.
If you define the static variable inside the class declaration then each include to that file would have a definition to that variable (which is against to the static meaning).
Because of that you have to define the static members in the .cpp.