What causes the Undefined symbol for x86_64 architecture "Build error?"

This is an excerpt from a program I am working on. I suspect this problem could be caused by this member of the Player class:

std::vector<std::list<Bid> > lBidding


The code results in the following build error:

g++ -o ./Debug/fudge @"/Users/andvik/MockUp/fudge/fudge.txt"-L.   
Undefined symbols for architecture x86_64:
"Player::lBidding", referenced from:
  Deal::bidding()     in MockUp_main.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
make[1]: *** [Debug/fudge] Error 1
make[1]: Leaving directory `/Users/andvik/MockUp/fudge'
make: *** [All] Error 2
make: Leaving directory `/Users/andvik/MockUp'
----------Build Ended----------
0 errors, 0 warnings


I'm sure this error has something to do with the static vector, as this was the last piece of code I added. My research has shown many different problems leading to similar errors, but none of them are related to the same code that I have.

Code: (I've trimmed a few concise lines of code that don't seem to apply. This should be minimal.)

#include <string>
#include <list>
#include <vector>

class Bid
short iLevel;
short iSuit;
Bid(short l, short s):iLevel(l),iSuit(s){};
bool operator ==(const Bid Other) const
    if(iLevel==Other.iLevel && iSuit==Other.iSuit)
    {return 1;}
    else{return 0;}
class Player
short iPos;
static std::vector<std::list<Bid> > lBidding;
Player(short p):iPos(p) {};

bool operator ==(const Player Other) const
    if(iPos == Other.iPos){return 1;}
    else{return 0;
class Deal
short iPass;
short iIteration;
Player pWest, pNorth, pEast, pSouth, pError;
Deal(): iPass(0), iIteration(0), pWest(0), pNorth(1), pEast(2), pSouth(3), pError(5){};
void bidding()
    Player pTemp(5);
    Bid bTemp, bPass;
    while(iPass < 3)
        pTemp = setPlayer();

                    if(pTemp == pError){break;} 

        if(bTemp == bPass){++iPass;}
Player setPlayer()
    switch(iIteration % 4)
        case 0: return pWest; break;
        case 1: return pNorth; break;
        case 2: return pEast; break;
        case 3: return pSouth; break;
    return pError;
int main(int argc, char **argv)
Deal deal;
printf("No debugging error.\n");
return 0;


So can someone tell me what is wrong with my code and why. By the way, if anyone is wondering what is the main part of their homemade bridge simulator.


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1 answer

The reason is that lBidding is static, but you are declaring and not implementing it. If you just added:

std::vector<std::list<Bid> > Player::lBidding;


to the end of the file, everything will compile with joy.

Since static variables are not part of the object, but instead of a class, you need to implement them once in the cpp file, usually by the convention name <classname> .cpp. It's not a good idea to put it in a .h file as it will implement it in every file that includes it and will lead to (justifiable) linker errors.



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