C 未定义对'的引用；snapend'；

当我试图用我现有的C语言知识在我的项目中实现

LLDP

功能时，我遇到了这个问题。编译程序给出了一个错误声明

/home/tiara/NetBeansProjects/CppApplication_2/main.c:212:对snapend的未定义引用`

生成此代码的代码段是

voidlldp_print(const u_char *p, u_int len)
{
    u_int16_t tlv;
    u_int8_t *ptr = (u_int8_t *)p, v = 0;
    int n, type, vlen, alen;

    printf("LLDP");

#define _ptrinc(_v) ptr += (_v); vlen -= (_v);

    for (n = 0; n < len;) {
        TCHECK2(*ptr, sizeof(tlv)); //HERE IS WHERE THE ERROR POINTS TO

编辑

TECHECK2
在此处的
interface.h
头文件中定义

任何建议都将不胜感激：）
snapend
在
interface.h
中声明。您还需要定义
snapend
。因此，要么put（从interface.h复制）

进入项目或链接到包含变量snapend的库中（我不知道您是从tcpdump获取头文件还是同时使用tcpdump中的.o文件或库）。
我们怎么知道
TCHECK2（）
的作用？这是你的宏吗？那么你应该包括定义。如果它不是您的，为什么要使用它？@alk我提供了头文件，其中定义了
TCHECK2
amd感谢您的帮助reply@unwind谢谢你的指点。我在问题：）中提供了定义
TCHECK2
的代码，所以现在当您移动并挖掘此代码时，您可以自己解决此问题，不是吗？然后您必须找到在tcpdump代码中定义
snapend
的位置。（为什么要从tcpdump代码中包含任意头文件？）外部常量u_char*snapend并且它确实成功地构建了。但是，当程序实际运行时，这会带来问题吗；声明可以在多个源文件中包含和重复，并且仍然引用同一个变量。定义不能包含多次。如果库中未定义snapend，则仅定义一次，通常在带有main（）的文件中。
#include <sys/param.h>
#include <sys/time.h>
#include <sys/socket.h>

#include <net/if.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/if_ether.h>
#include <netinet/ether.h>
#include <arpa/inet.h>

#include <ctype.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#include "addrtoname.h"
#include "extract.h"
#include "interface.h"
#include "afnum.h"

/*  $OpenBSD: interface.h,v 1.62 2014/01/11 04:35:52 lteo Exp $ */

/*
 * Copyright (c) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
 *  The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that: (1) source code distributions
 * retain the above copyright notice and this paragraph in its entirety, (2)
 * distributions including binary code include the above copyright notice and
 * this paragraph in its entirety in the documentation or other materials
 * provided with the distribution, and (3) all advertising materials mentioning
 * features or use of this software display the following acknowledgement:
 * ``This product includes software developed by the University of California,
 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
 * the University nor the names of its contributors may be used to endorse
 * or promote products derived from this software without specific prior
 * written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * @(#) $Id: interface.h,v 1.62 2014/01/11 04:35:52 lteo Exp $ (LBL)
 */

#ifndef tcpdump_interface_h
#define tcpdump_interface_h

#include "gnuc.h"
#ifdef HAVE_OS_PROTO_H
#include "os-proto.h"
#endif

struct tok {
    int v;          /* value */
    char *s;        /* string */
};

extern int aflag;       /* translate network and broadcast addresses */
extern int dflag;       /* print filter code */
extern int eflag;       /* print ethernet header */
extern int fflag;       /* don't translate "foreign" IP address */
extern int Iflag;       /* include interface in output */
extern int nflag;       /* leave addresses as numbers */
extern int Nflag;       /* remove domains from printed host names */
extern int oflag;       /* OS fingerprint */
extern int qflag;       /* quick (shorter) output */
extern int Sflag;       /* print raw TCP sequence numbers */
extern int tflag;       /* print packet arrival time */
extern int vflag;       /* verbose */
extern int xflag;       /* print packet in hex */
extern int Xflag;       /* print packet in hex/ascii */

extern int packettype;      /* as specified by -T */
extern char *device;        /* as specified by -i  */
#define PT_VAT      1   /* Visual Audio Tool */
#define PT_WB       2   /* distributed White Board */
#define PT_RPC      3   /* Remote Procedure Call */
#define PT_RTP      4   /* Real-Time Applications protocol */
#define PT_RTCP     5   /* Real-Time Applications control protocol */
#define PT_CNFP     6   /* Cisco NetFlow protocol */
#define PT_VRRP     7   /* Virtual Router Redundancy protocol */
#define PT_TCP      8   /* TCP */

#ifndef min
#define min(a,b) ((a)>(b)?(b):(a))
#endif
#ifndef max
#define max(a,b) ((b)>(a)?(b):(a))
#endif

/*
 * The default snapshot length.  This value allows most printers to print
 * useful information while keeping the amount of unwanted data down.
 * In particular, it allows ethernet, tcp/ip headers, and a small amount
 * of data, or to capture IPv6 and TCP headers after pflog encapsulation.
 */
#define DEFAULT_SNAPLEN 116
#define IEEE802_11_SNAPLEN (DEFAULT_SNAPLEN + 30)
#define IEEE802_11_RADIO_SNAPLEN (IEEE802_11_SNAPLEN + 64)

#ifndef BIG_ENDIAN
#define BIG_ENDIAN 4321
#define LITTLE_ENDIAN 1234
#endif

#ifdef ETHER_HEADER_HAS_EA
#define ESRC(ep) ((ep)->ether_shost.ether_addr_octet)
#define EDST(ep) ((ep)->ether_dhost.ether_addr_octet)
#else
#define ESRC(ep) ((ep)->ether_shost)
#define EDST(ep) ((ep)->ether_dhost)
#endif

#ifdef ETHER_ARP_HAS_X
#define SHA(ap) ((ap)->arp_xsha)
#define THA(ap) ((ap)->arp_xtha)
#define SPA(ap) ((ap)->arp_xspa)
#define TPA(ap) ((ap)->arp_xtpa)
#else
#ifdef ETHER_ARP_HAS_EA
#define SHA(ap) ((ap)->arp_sha.ether_addr_octet)
#define THA(ap) ((ap)->arp_tha.ether_addr_octet)
#else
#define SHA(ap) ((ap)->arp_sha)
#define THA(ap) ((ap)->arp_tha)
#endif
#define SPA(ap) ((ap)->arp_spa)
#define TPA(ap) ((ap)->arp_tpa)
#endif

#ifndef NTOHL
#define NTOHL(x)    (x) = ntohl(x)
#define NTOHS(x)    (x) = ntohs(x)
#define HTONL(x)    (x) = htonl(x)
#define HTONS(x)    (x) = htons(x)
#endif
#endif

extern char *program_name;  /* used to generate self-identifying messages */

extern int32_t thiszone;    /* seconds offset from gmt to local time */

extern int snaplen;
/* global pointers to beginning and end of current packet (during printing) */
extern const u_char *packetp;
extern const u_char *snapend;

/*
 * True if  "l" bytes of "var" were captured.
 *
 * The "snapend - (l) <= snapend" checks to make sure "l" isn't so large
 * that "snapend - (l)" underflows.
 *
 * The check is for <= rather than < because "l" might be 0.
 */
#define TTEST2(var, l) (snapend - (l) <= snapend && \
            (const u_char *)&(var) <= snapend - (l))

/* True if "var" was captured */
#define TTEST(var) TTEST2(var, sizeof(var))

/* Bail if "l" bytes of "var" were not captured */
#define TCHECK2(var, l) if (!TTEST2(var, l)) goto trunc

/* Bail if "var" was not captured */
#define TCHECK(var) TCHECK2(var, sizeof(var))

struct timeval;
struct bpf_timeval;

extern void ts_print(const struct bpf_timeval *);

extern int fn_print(const u_char *, const u_char *);
extern int fn_printn(const u_char *, u_int, const u_char *);
extern void relts_print(int);
extern const char *tok2str(const struct tok *, const char *, int);
extern char *dnaddr_string(u_short);
extern void safeputs(const char *);
extern void safeputchar(int);
extern void printb(char *, unsigned short, char *);

extern void wrapup(int);

extern __dead void error(const char *, ...)
    __attribute__((__format__ (printf, 1, 2)));
extern void warning(const char *, ...)
    __attribute__ ((__format__ (printf, 1, 2)));

extern char *read_infile(char *);
extern char *copy_argv(char * const *);

extern char *isonsap_string(const u_char *);
extern char *llcsap_string(u_char);
extern char *protoid_string(const u_char *);
extern char *dnname_string(u_short);
extern char *dnnum_string(u_short);

/* The printer routines. */

struct pcap_pkthdr;

extern int ether_encap_print(u_short, const u_char *, u_int, u_int);
extern int llc_print(const u_char *, u_int, u_int, const u_char *,
    const u_char *);
extern int pppoe_if_print(u_short, const u_char *, u_int, u_int);
extern void aarp_print(const u_char *, u_int);
extern void arp_print(const u_char *, u_int, u_int);
extern void atalk_print(const u_char *, u_int);
extern void atalk_print_llap(const u_char *, u_int);
extern void atm_if_print(u_char *, const struct pcap_pkthdr *, const u_char *);
extern void bootp_print(const u_char *, u_int, u_short, u_short);
extern void bgp_print(const u_char *, int);
extern void decnet_print(const u_char *, u_int, u_int);
extern void default_print(const u_char *, u_int);
extern void default_print_unaligned(const u_char *, u_int);
extern void dvmrp_print(const u_char *, u_int);
extern void egp_print(const u_char *, u_int, const u_char *);
extern void enc_if_print(u_char *, const struct pcap_pkthdr *, const u_char *);
extern void pflog_if_print(u_char *, const struct pcap_pkthdr *,
    const u_char *);
extern void pflog_old_if_print(u_char *, const struct pcap_pkthdr *,
    const u_char *);
extern void pfsync_if_print(u_char *, const struct pcap_pkthdr *,
    const u_char *);
extern void pfsync_ip_print(const u_char *, u_int, const u_char *);
extern void ether_if_print(u_char *, const struct pcap_pkthdr *,
    const u_char *);
extern void fddi_if_print(u_char *, const struct pcap_pkthdr *, const u_char *);
extern void ppp_ether_if_print(u_char *, const struct pcap_pkthdr *,
    const u_char *);
extern void gre_print(const u_char *, u_int);
extern void icmp_print(const u_char *, u_int, const u_char *);
extern void ieee802_11_if_print(u_char *, const struct pcap_pkthdr *,
    const u_char *);
extern void ieee802_11_radio_if_print(u_char *, const struct pcap_pkthdr *,
    const u_char *);
extern void iapp_print(const u_char *, u_int);
extern void igrp_print(const u_char *, u_int, const u_char *);
extern void ip_print(const u_char *, u_int);
extern void ipx_print(const u_char *, u_int);
extern void isoclns_print(const u_char *, u_int, u_int, const u_char *,
    const u_char *);
extern void krb_print(const u_char *, u_int);
extern void netbeui_print(u_short, const u_char *, const u_char *);
extern void ipx_netbios_print(const u_char *, const u_char *);
extern void nbt_tcp_print(const u_char *, int);
extern void nbt_udp137_print(const u_char *data, int);
extern void nbt_udp138_print(const u_char *data, int);
extern char *smb_errstr(int, int);
extern void print_data(const unsigned char *, int);
extern void l2tp_print(const u_char *dat, u_int length);
extern void vrrp_print(const u_char *bp, u_int len, int ttl);
extern void carp_print(const u_char *bp, u_int len, int ttl);
extern void hsrp_print(const u_char *, u_int);
extern void vqp_print(const u_char *, u_int);
extern void nfsreply_print(const u_char *, u_int, const u_char *);
extern void nfsreq_print(const u_char *, u_int, const u_char *);
extern void ns_print(const u_char *, u_int, int);
extern void ntp_print(const u_char *, u_int);
extern void loop_if_print(u_char *, const struct pcap_pkthdr *, const u_char *);
extern void null_if_print(u_char *, const struct pcap_pkthdr *, const u_char *);
extern void ospf_print(const u_char *, u_int, const u_char *);
extern void mobile_print(const u_char *, u_int);
extern void pim_print(const u_char *, u_int);
extern void ppp_if_print(u_char *, const struct pcap_pkthdr *, const u_char *);
extern void ppp_hdlc_print(const u_char *, int);
extern void raw_if_print(u_char *, const struct pcap_pkthdr *, const u_char *);
extern void rip_print(const u_char *, u_int);
extern void sl_if_print(u_char *, const struct pcap_pkthdr *, const u_char *);
extern void sl_bsdos_if_print(u_char *, const struct pcap_pkthdr *,
    const u_char *);
extern void snmp_print(const u_char *, u_int);
extern void sunrpcrequest_print(const u_char *, u_int, const u_char *);
extern void cnfp_print(const u_char *, u_int, const u_char *);
extern void tcp_print(const u_char *, u_int, const u_char *);
extern void tftp_print(const u_char *, u_int);
extern void timed_print(const u_char *, u_int);
extern void udp_print(const u_char *, u_int, const u_char *);
extern void wb_print(const void *, u_int);
extern void ike_print(const u_char *, u_int);
extern void udpencap_print(const u_char *, u_int, const u_char *);
extern void ah_print(const u_char *, u_int, const u_char *);
extern void esp_print(const u_char *, u_int, const u_char *);
extern void cdp_print(const u_char *, u_int, u_int, const u_char *,
    const u_char *);
extern void stp_print(const u_char *, u_int);
extern void radius_print(const u_char *, u_int);
extern void lwres_print(const u_char *, u_int);
extern void ether_print(const u_char *, u_int);
extern void etherip_print(const u_char *, u_int, u_int, const u_char *);
extern void ipcomp_print(const u_char *, u_int, const u_char *);
extern void mpls_print(const u_char *, u_int);
extern void lldp_print(const u_char *, u_int);
extern void slow_print(const u_char *, u_int);
extern void gtp_print(const u_char *, u_int, u_short, u_short);

#ifdef INET6
extern void ip6_print(const u_char *, int);
extern void ip6_opt_print(const u_char *, int);
extern int hbhopt_print(const u_char *);
extern int dstopt_print(const u_char *);
extern int frag6_print(const u_char *, const u_char *);
extern void icmp6_print(const u_char *, u_int, const u_char *);
extern void ripng_print(const u_char *, int);
extern int rt6_print(const u_char *, const u_char *);
extern void ospf6_print(const u_char *, u_int);
extern void dhcp6_print(const u_char *, u_int, u_short, u_short);
#endif /*INET6*/

extern u_short in_cksum(const u_short *addr, register int len, int csum);

extern const u_char *snapend;

/*
 * True if  "l" bytes of "var" were captured.
 *
 * The "snapend - (l) <= snapend" checks to make sure "l" isn't so large
 * that "snapend - (l)" underflows.
 *
 * The check is for <= rather than < because "l" might be 0.
 */
#define TTEST2(var, l) (snapend - (l) <= snapend && \
            (const u_char *)&(var) <= snapend - (l))

/* True if "var" was captured */
#define TTEST(var) TTEST2(var, sizeof(var))

/* Bail if "l" bytes of "var" were not captured */
#define TCHECK2(var, l) if (!TTEST2(var, l)) goto trunc

/* Bail if "var" was not captured */
#define TCHECK(var) TCHECK2(var, sizeof(var))

const u_char *snapend;