Undefined Reference Using Vectors

Question

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I am getting this undefined reference error:

/tmp/ccYnTr05.o: In function `TourManager::addCity(City)':
tsp.cpp:(.text._ZN11TourManager7addCityE4City[TourManager::addCity(City)]+0x1c): undefined reference to `TourManager::destinationCities'
/tmp/ccYnTr05.o: In function `TourManager::getCity(int)':
tsp.cpp:(.text._ZN11TourManager7getCityEi[TourManager::getCity(int)]+0x14): undefined reference to `TourManager::destinationCities'
/tmp/ccYnTr05.o: In function `TourManager::numberOfCities()':
tsp.cpp:(.text._ZN11TourManager14numberOfCitiesEv[TourManager::numberOfCities()]+0x5): undefined reference to `TourManager::destinationCities'
collect2: ld returned 1 exit status

Here is the code:

C++

class TourManager
{
private:
    
    static vector<City> destinationCities;
    
public:
    
    static void addCity(City city)
    {
        destinationCities.push_back(city);
    }
    
    static City getCity(int index)
    {
        return (City)destinationCities.at(index);
    }
    
    static int numberOfCities()
    {
        return (int)destinationCities.size();
    }
};

I don't know what this error means and I certainly don't know how to fix it. Any help will be appreciated.

Posted 27-Nov-13 14:19pm

Heath Branum

Updated 27-Nov-13 14:21pm

v2

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Comments

Sergey Alexandrovich Kryukov 27-Nov-13 22:05pm

The source of your problem is not shown in your code sample, as simple as that.
Do this: 1) reduce test application to bare minimum; but it still show the exception; 2) catch all exceptions on the very top stack frame of the thread, 3) find out the whole path of exception propagation; 4) if you cannot resolve the problem, show involved code; or:
1a) or do the same as above but from the debuggert, 2a) see Call Stack (this is the debug window), 3a) if you cannot resolve the problem, show involved code...
—SA

4 solutions

Solution 1

Where do you allocate the memory for destinationCities?

You need to initialize destinationCities to a new vector<city> before you can add data to it, otherwise its the same as a null pointer.

Posted 27-Nov-13 14:25pm

Ron Beyer

Comments

Heath Branum 27-Nov-13 20:29pm

But I just need an empty vector. I don't need to put any values in it until addCity function.

Heath Branum 27-Nov-13 20:31pm

Also I have done the same thing in other classes just fine without any errors. Vectors don't need to be assigned a size because they allocate memory dynamically.

Stefan_Lang 28-Nov-13 5:57am

Since you declared this member variable as static, you do need to actually declare it elsewhere. it's like declaring a global variable as "extern" in a header without actually defining it anywhere!

Philippe Mori 30-Nov-13 9:13am

Not exactly the same as a null pointer...

Solution 4

Ron Beyer is right in what he says in solution 1. Any static data members of a class must somewhere be defined. You just need to add a line

C++

vector<city> TourManager::destinationCities;

somewhere in a cpp file. You are correct in assuming that a vector knows how to initialize itself. That applies if you define a vector as an instance member of a class. In your case, however, you are declaring a static members, and all static data members must be defined somewhere. That is the reason it worked in your previous experience and why it didn't in this particular case.

Posted 27-Nov-13 23:11pm

nv3

Updated 28-Nov-13 1:44am

v2

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Albert Holguin · Accepted Answer · 2013-11-27T17:11:00

You probably need to define/instantiate your static outside of the class. Since he's independent of instance (static), he needs to be defined outside of the class to actually exist, otherwise he's just been declared (usually you need to do the instantiate inside of the cpp file, if I remember correctly, you're not allowed to do it in a header file).

Same problem as this:
http://stackoverflow.com/questions/272900/undefined-reference-to-static-class-member[^]

User 59241 · Accepted Answer · 2013-11-27T15:58:00

Solution 2

Code looks fine and compiles in vs2010.
Looks like you are missing vector.
You need lines:

C++

#include <vector>;

using namespace std;

Posted 27-Nov-13 15:58pm

User 59241

v2

Comments

Philippe Mori 30-Nov-13 9:16am

The static variable definition is missing and code does not look so fine. You don't want a cast in getCity and you probably want reference (or const reference) for arguments and returns value and in C++, C style cast should not be used (static_cast should be used instead fur numberOfCities function).

Undefined Reference Using Vectors

4 solutions

Solution 3

Solution 2

Solution 1

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