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symbol not found

ASCII14 (44)
Whenever I run this code, I get this error:

Undefined symbols for architecture x86_64:
"Producer::lifespan", referenced from:
Producer::init_producer(std::string, int, int) in Producer.o
"Producer::birth_rate", referenced from:
Producer::init_producer(std::string, int, int) in Producer.o
"Producer::name", referenced from:
Producer::init_producer(std::string, int, int) in Producer.o
"Consumer::lifespan", referenced from:
Consumer::init_consumer(int, std::string, int, int) in Consumer.o
"Consumer::birth_rate", referenced from:
Consumer::init_consumer(int, std::string, int, int) in Consumer.o
"Consumer::name", referenced from:
Consumer::init_consumer(int, std::string, int, int) in Consumer.o
"Consumer::level", referenced from:
Consumer::init_consumer(int, std::string, int, int) in Consumer.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Consumer.h 
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  #ifndef Ecological_Mapping_Consumer_h
#define Ecological_Mapping_Consumer_h

#include <string>

using namespace std;

class Consumer
{
public:
    
    static int level;
    static string name;
    static int birth_rate;
    static int lifespan;
    
    static void init_consumer(int lv, string nm, int br, int ls);
    static void remv_consumer();
};

#endif


Consumer.cpp 
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#include <iostream>
#include "Consumer.h"

void Consumer::init_consumer(int lv, string nm, int br, int ls)
{
    Consumer::level = lv;
    Consumer::name = nm;
    Consumer::birth_rate = br;
    Consumer::lifespan = ls;
}
void Consumer::remv_consumer()
{
    
}


Producer.h 
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#ifndef Ecological_Mapping_Producer_h
#define Ecological_Mapping_Producer_h

#include <string>

using namespace std;

class Producer 
{
public: 
    
    static string name;
    static int birth_rate;
    static int lifespan;
    
    static void init_producer(string nm, int br, int ls);
    static void remv_producer();
};

#endif


Producer.cpp 
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#include <iostream>
#include "Producer.h"

void Producer::init_producer(string nm, int br, int ls)
{
    Producer::name = nm;
    Producer::birth_rate = br;
    Producer::lifespan = ls;
}
void Producer::remv_producer()
{
    
}


main.cpp 
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#include <iostream>
#include <string>

#include "Producer.h"
#include "Consumer.h"


using namespace std;

string s_temp_1;
string s_temp_2;
int i_temp_1;
int i_temp_2;
int i_temp_3;
int i_temp_4;

int main ()
{
    cout << "ECOLOGICAL MAPPING:" << endl;
    cout << "Name of Organsim:" << endl;
    cin >> s_temp_1;
    cout << "Producer or Consumer:" << endl;
    cin >> s_temp_2;
    cout << "Birth Rate of Organsim (Per Year):" << endl;
    cin >> i_temp_1;
    cout << "Average Lifespan of Organsim (In Years):" << endl;
    cin >> i_temp_2;
    if(s_temp_2 != "producer" || s_temp_2 != "Producer" || s_temp_2 != "p" || s_temp_2 != "P" )
    {
        cout << "Primary, Secondary, Tertiary, or Quarternary: (1,2,3,4)" << endl;
        cin >> i_temp_3;
        Consumer::init_consumer(i_temp_3, s_temp_1, i_temp_1, i_temp_2);
    }
    else
    {
        
    }
}

ASCII14 (44)
i've done projects like this before, but I don't know what i'm doing wrong. Any help appreciated. Thanks!
Daleth (1030)
Because static members area shared among objects, they are not defined for each object. You have to define them in a separate place, most commonly the source file where you also define the methods. So for example in your Consumer.cpp file, you would have:
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#include "Consumer.h"

int Consumer::level;
std::string Consumer::name;
int Consumer::birth_rate;
int Consumer::lifespan;

Note that you do not include static when defining static members.

By the way, if you have a class whose members are all public and static... You may as well just use a namespace.
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