C++网络编程问题，附部分代码

/*下边实现tcp数据包分析的函数定义tcp_protocol_packet_callback*/
void tcp_protocol_packet_callback(u_char argument,const struct pcap_pkthdr
packet_header,const u_char* packet_content)
{

     struct tcp_header *tcp_protocol ;     /*tcp协议变量*/
     u_char flags;                          /*标记*/
     int header_length;                  /*头长度*/
     u_short source_port;           /*源端口*/
     u_short destination_port;   /*目的端口*/
     u_short windows;                /*窗口大小*/
     u_short urgent_pointer;     /*紧急指针*/
     u_int sequence;                 /*序列号*/
     u_int acknowledgement;   /*确认号*/
     u_int16_t   checksum;       /*检验和*/
     tcp_protocol=(struct tcp_header *) (packet_content+14+20);  /*获得tcp首部内容*/

为什么这里tcp_protocol=(struct tcp_header *) (packet_content+14+20)是14+20啊

MAC帧头14字节，IP头20字节

https://blog.csdn.net/liwenxia626/article/details/80823291