UNIX for Dummies Questions & Answers

#include <dirent.h>
#include <errno.h>
#include <fnmatch.h>
#include <netinet/in.h>
#include <syslog.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <utime.h>

#include <bbftpd.h>
#include <common.h>
#include <daemon.h>
#include <daemon_proto.h>
#include <status.h>
#include <structures.h>

extern int  transferoption ;
extern int  outcontrolsock ;
extern	int	recvcontrolto ;
extern	int	sendcontrolto ;

int bbftpd_list(char *pattern,char *logmessage) 
{

    char    *filelist ;
    int     filelistlen ;
    int     retcode ;
    char    send_buffer[MINMESSLEN] ;
    struct message *msg ;
    
    
    if ( (retcode = bbftpd_retrlistdir(pattern,&filelist,&filelistlen,logmessage) ) < 0) {
        reply(MSG_BAD_NO_RETRY,logmessage) ;
        return 0 ;
    } else if ( retcode > 0 ) {
        reply(MSG_BAD,logmessage) ;
        return 0 ;
    } else {
        msg = (struct message *) send_buffer ;
        msg->code = MSG_LIST_REPL_V2 ;
#ifndef WORDS_BIGENDIAN
        msg->msglen = ntohl(filelistlen) ;
#else 
        msg->msglen = filelistlen ;
#endif
        if ( writemessage(outcontrolsock,send_buffer,MINMESSLEN,recvcontrolto) < 0 ) {
            syslog(BBFTPD_ERR,"Error sending LISTREPL_V2 part 1") ;
            FREE(filelist) ;
            return -1 ;
        }
        if (filelistlen != 0 ) {
            if ( writemessage(outcontrolsock,filelist,filelistlen,recvcontrolto) < 0 ) {
                FREE(filelist) ;
                syslog(BBFTPD_ERR,"Error sending filelist") ;
                return -1 ;
            }
            FREE(filelist) ;
            return 0 ;
        }
        return 0 ;
    }
}

Here are the errors I received (the affected lines are in bold):
bbftpd_list.c:84:13: error: use of undeclared identifier 'NULL'
            FREE(filelist) ;
            ^
../includes/common.h:95:25: note: expanded from macro 'FREE'
#define FREE(X) if(X != NULL) { free(X), X=NULL;}
                        ^
bbftpd_list.c:84:13: warning: implicit declaration of function 'free' is invalid
      in C99 [-Wimplicit-function-declaration]
            FREE(filelist) ;
            ^
../includes/common.h:95:33: note: expanded from macro 'FREE'
#define FREE(X) if(X != NULL) { free(X), X=NULL;}
                                ^
bbftpd_list.c:84:13: error: use of undeclared identifier 'NULL'
            FREE(filelist) ;
            ^
../includes/common.h:95:44: note: expanded from macro 'FREE'
#define FREE(X) if(X != NULL) { free(X), X=NULL;}
                                           ^
bbftpd_list.c:89:17: error: use of undeclared identifier 'NULL'
                FREE(filelist) ;
                ^
../includes/common.h:95:25: note: expanded from macro 'FREE'
#define FREE(X) if(X != NULL) { free(X), X=NULL;}
                        ^
bbftpd_list.c:89:17: error: use of undeclared identifier 'NULL'
                FREE(filelist) ;
                ^
../includes/common.h:95:44: note: expanded from macro 'FREE'
#define FREE(X) if(X != NULL) { free(X), X=NULL;}
                                           ^
bbftpd_list.c:93:13: error: use of undeclared identifier 'NULL'
            FREE(filelist) ;
            ^
../includes/common.h:95:25: note: expanded from macro 'FREE'
#define FREE(X) if(X != NULL) { free(X), X=NULL;}
                        ^
bbftpd_list.c:93:13: error: use of undeclared identifier 'NULL'
            FREE(filelist) ;