g++: undefined reference to member variable

Question

when I compile this code I get the following errors:

email2.cpp:27: undefined reference to `email_client::payload_text'

email2.cpp:28: undefined reference to `email_client::payload_text'

email2.cpp:29: undefined reference to `email_client::payload_text'

email2.cpp:30: undefined reference to `email_client::payload_text'

email2.cpp:31: undefined reference to `email_client::payload_text'

/tmp/ccE0wEII.o:email2.cpp:32: more undefined references to `email_client::payload_text' follow collect2: error: ld returned 1 exit status

my declaration signature matches my definition one, so I'm not sure what to make of these errors. please help.

cpp

#include <curl/curl.h>
#include <cstdio>
#include <string>
#include "email.h"

char* cat_char(std::string first, const char* second) {
        char* tmp = new char[first.size()];
        strcpy(tmp, first.c_str());
        strcat(tmp, second);
        strcat(tmp, "\r\n");
        return tmp;
}

char* cat_char(std::string first) {
        char* tmp = new char[first.size()];
        strcpy(tmp, first.c_str());
        strcat(tmp, "\r\n");
        return tmp;
}



email_client::email_client(message msg, std::string TO, std::string FROM):
        m_to(TO.c_str()),
        m_from(FROM.c_str())
         {
                payload_text[0] = cat_char("To: ", TO.c_str());
                payload_text[1] = cat_char("From: ", m_from);
                payload_text[2] = cat_char("Subject: ", msg.subject.c_str());
                payload_text[3] = cat_char("", "\r\n"); 
                payload_text[4] = cat_char(msg.body, "\r\n");
                payload_text[5] = NULL;
        };

header

#include <string>
#include <cstring>
#include <cstdio>

struct message{
        std::string subject;
        std::string body;
};

char* cat_char(std::string first, const char* second);

char* cat_char(std::string first);

class email_client{
                const char* m_to;
                const char* m_from;
                static char* payload_text[];
        public:
                email_client(message msg, std::string TO, std::string FROM="test@stest.com");
};