Placing a class object inside a vector?

I noticed that I can place a Class inside a vector; here is my program, where I am receiving the following error:

/out:blackjack.exe
blackjack.obj
blackjack.obj : error LNK2019: unresolved external symbol "private: static class
 std::vector<class Card,class std::allocator<class Card> > Card::Cards" (?Cards@
Card@@0V?$vector@VCard@@V?$allocator@VCard@@@std@@@std@@A) referenced in functio
n "public: static void __cdecl Card::blankCard(void)" (?blankCard@Card@@SAXXZ)
blackjack.exe : fatal error LNK1120: 1 unresolved externals

The issue is inside the `blankcard() function, where I'm trying to create a new class instance, and put it into the vector.

Can someone please read the code tell me my issue and give me a good example in how to do this? Thank you.

#include <iostream>
#include <vector>
#include <string>
using namespace std;

class Card
{
  private:
    string suit;
    int number;
    static vector<Card> Cards;

  public:
    Card::Card();
    Card::Card(string cardS, int cardV);
    static void createCards(); 
    static void blankCard();    
};


int main()
{
  Card::blankCard();
  return 0;
}

Card::Card(){};
Card::Card(string cardS, int cardV){};

void Card::blankCard()
{
   int temp = 1;
   int cardValue; 
   string suit;
   int suitCount = 1;

   for(int i = 1; i < 52; i++)
   {
     if(temp == 1 || temp > 13)
     {
       temp = 1;
       cardValue = temp;
       temp ++;
     }
     else if(temp > 1)
     { 
       cardValue = temp;
       temp ++;
     }

     if(suitCount <= 13)
     {
       suit = "spade";
       suitCount++;
     }
     else if( suitCount >= 14 && suitCount <= 26)
     {
       suit = "club";
       suitCount++;
     }
     else if(suitCount >= 27 && suitCount <= 39)
     {
       suit = "heart";
       suitCount++;
     }
     else if(suitCount >= 40 && suitCount <= 52)  
     {
       suit = "diamonds";
       suitCount++;
     }     

     Card a = Card(suit, cardValue);
     Cards.push_back(a);
   }
}

回答1:

You are declaring the static member Cards inside the class definition, but you aren't defining it anywhere. Add a definition after the class definition:

vector<Card> Card::Cards;

回答2:

You'll have to instantiate the vector somewhere as it's a static. Basically, you want something like:

std::vector<Card> Card::Cards;

somewhere in your code.

回答3:

Your cards vector is defined as static. That means it is effectively a global variable that you must define. This can be done by putting the following after the class definition of Card: