Re: undefined reference

Here is the error i am getting:

/tmp/ccu9LP0x.o: In function
`command::tokenizer(std::basic_string<char, std::char_traits<char>,
std::allocator<char> >, std::vector<std::basic_string<char,
std::char_traits<char>, std::allocator<char> >,
std::allocator<std::basic_string<char, std::char_traits<char>,
std::allocator<char> > > >, std::basic_string<char,
std::char_traits<char>, std::allocator<char> >)':
command.cpp:(.gnu.linkonce.t._ZN7command9tokenizerESsSt6vectorISsSaISsEESs+0x59):
undefined reference to `command::com'
command.cpp:(.gnu.linkonce.t._ZN7command9tokenizerESsSt6vectorISsSaISsEESs+0xe9):
undefined reference to `command::com'
collect2: ld returned 1 exit status

Here is the source code:

#include <iostream>
#include <string>
#include <vector>

using namespace std;

class command {
       public:
               static void tokenizer(string str, vector<string> words, string
delimiter){
                       string::size_type pos1 = 0;
                       string::size_type pos2 = str.find_first_of(delimiter);
                       com.push_back(str.substr(pos1 ,pos2 - 1));
                       pos1 = pos2 + 1;
                       while(pos2 != string::npos){
                               pos2 = str.find_first_of(delimiter, pos2);
                               com.push_back(str.substr(pos1 ,pos2 - 1));
                               pos1 = pos2 + 1;
                       }
               }
               static void getCommand(string c){
                       tokenizer(c, com, " ");
                       if(com.size() == 1){
                       } else if(com.size() == 2){
                       } else { }
               }
       private:
               static vector<string> com;

};

int main()
{
       vector<string> test;
       string t = "hello how are you doing today";
       command::tokenizer(t, test, " ");
       cout << "there are " << test.size() << " words in that string.\n";
       int i;
       for(i = 0; i < test.size(); i++){
               cout << test[i];
       }
       return 0;
}

Thanks in advance.