Question

I keep getting this error: expected specifier-qualifier-list before ‘tcp_seq’ in my header file.

Here is the header file:

#include <netinet/ip.h>

/* TCP header */
struct sniff_tcp {
    u_short th_sport; /* source port */
    u_short th_dport; /* destination port */
    tcp_seq th_seq; /* sequence number */
    tcp_seq th_ack; /* acknowledgement number */
    #if BYTE_ORDER == LITTLE_ENDIAN
    u_int th_x2:4, /* (unused) */
    th_off:4; /* data offset */
    #endif
    #if BYTE_ORDER == BIG_ENDIAN
    u_int th_off:4, /* data offset */
    th_x2:4; /* (unused) */
    #endif
    u_char th_flags;
    #define TH_FIN 0x01
    #define TH_SYN 0x02
    #define TH_RST 0x04
    #define TH_PUSH 0x08
    #define TH_ACK 0x10
    #define TH_URG 0x20
    #define TH_ECE 0x40
    #define TH_CWR 0x80
    #define TH_FLAGS (TH_FIN|TH_SYN|TH_RST|TH_ACK|TH_URG|TH_ECE|TH_CWR)
    u_short th_win; /* window */
    u_short th; /* checksum */
    u_short th_urp; /* urgent pointer */
};


/* Ethernet header */
struct sniff_ethernet {
    u_char ether_dhost[ETHER_ADDR_LEN]; /* Destination host address */
    u_char ether_shost[ETHER_ADDR_LEN]; /* Source host address */
    u_short ether_type;                 /* IP? ARP? RARP? etc */
};

/* IP header */
struct sniff_ip {
    #if BYTE_ORDER == LITTLE_ENDIAN
    u_int ip_hl:4,                      /* header length */
    ip_v:4;                             /* version */
    #if BYTE_ORDER == BIG_ENDIAN
    u_int ip_v:4,                       /* version */
    ip_hl:4;                            /* header length */
    #endif
    #endif                              /* not _IP_VHL */
    u_char ip_tos;                      /* type of service */
    u_short ip_len;                     /* total length */
    u_short ip_id;                      /* identification */
    u_short ip_off;                     /* fragment offset field */
    #define IP_RF 0x8000                /* reserved fragment flag */
    #define IP_DF 0x4000                /* dont fragment flag */
    #define IP_MF 0x2000                /* more fragments flag */
    #define IP_OFFMASK 0x1fff           /* mask for fragmenting bits */
    u_char ip_ttl;                      /* time to live */
    u_char ip_p;                        /* protocol */
    u_short ip_sum;                     /* checksum */
    struct in_addr ip_src,ip_dst;       /* source and dest address */
};

I can’t get to the bottom of it, even with google.

I hope someone has some suggestions.

Many thanks in advance,

Answer 1

Looks like you copied copied the tcphdr structure from netinet/tcp.h.

The error message you get is simply a complicated way of saying that the tcp_seq type is not known. For me, this is defined by netinet/tcp.h if the preprocessor macro __FAVOR_BSD is defined.

Alternatively, you could just use u_long or any other unsigned 32bit integer type.