non-aggregate type `const pcap_pkthdr*'??? [复制链接]

request for member `caplen' in `packet_header', which is of
  non-aggregate type `const pcap_pkthdr*'

我在程序里定义了pcap_pkthdr 类型的变量 packet_header
然后用packet_header.caplen时报上面的错误

/usr/local/include/pcap.h里是这样定义pcap_pkthdr的
struct pcap_pkthdr {
  struct timeval ts;   /* time stamp */
  bpf_u_int32 caplen;   /* length of portion present */
  bpf_u_int32 len;   /* length this packet (off wire) */
};
请指点一下到底是哪出了问题,谢谢