I'm working throurgh a project with pcap and wireless. Following an example posted in response to oe of my earlier questions I am trying to extract the mac addresses from wireless frames. I have created structures for the radiotap header and a basic management frame. For some reason when it comes to trying to output the mac addresses I am printing out the wrong data. When I compare to wireshark I don't see why the radio tap data is printing out correctly but the mac addresses are not. I don't see any additional padding in the hex dump that wireshark displays when i look at the packets and compare the packets that I have captured. I am somewhat famialar with c but not an expert so maybe I am not using the pointers and structures properly could someone help show me what I am doing wrong?

Thanks, Quentin

//  main.c
//  MacSniffer
//


#include <pcap.h>
#include <string.h>
#include <stdlib.h>

#define MAXBYTES2CAPTURE 65535

#ifdef WORDS_BIGENDIAN
typedef struct frame_control
{
    unsigned int subtype:4; /*frame subtype field*/
    unsigned int protoVer:2; /*frame type field*/
    unsigned int version:2; /*protocol version*/

    unsigned int order:1;  
    unsigned int protected:1;
    unsigned int moreDate:1;
    unsigned int power_management:1;

    unsigned int retry:1; 
    unsigned int moreFrag:1;
    unsigned int fromDS:1;
    unsigned int toDS:1;
}frame_control;

struct ieee80211_radiotap_header{
    u_int8_t it_version;
    u_int8_t it_pad;
    u_int16_t it_len;
    u_int32_t it_present;
    u_int64_t MAC_timestamp;
    u_int8_t flags;
    u_int8_t dataRate;
    u_int16_t channelfrequency;
    u_int16_t channFreq_pad;
    u_int16_t channelType;
    u_int16_t channType_pad;
    u_int8_t ssiSignal;
    u_int8_t ssiNoise;
    u_int8_t antenna;
};

#else
typedef struct frame_control
{
    unsigned int protoVer:2; /* protocol version*/
    unsigned int type:2; /*frame type field (Management,Control,Data)*/
    unsigned int subtype:4; /* frame subtype*/

    unsigned int toDS:1; /* frame coming from Distribution system */
    unsigned int fromDS:1; /*frame coming from Distribution system */
    unsigned int moreFrag:1; /* More fragments?*/
    unsigned int retry:1; /*was this frame retransmitted*/

    unsigned int powMgt:1; /*Power Management*/
    unsigned int moreDate:1; /*More Date*/
    unsigned int protectedData:1; /*Protected Data*/
    unsigned int order:1; /*Order*/
}frame_control;

struct ieee80211_radiotap_header{
    u_int8_t it_version;
    u_int8_t it_pad;
    u_int16_t it_len;
    u_int32_t it_present;
    u_int64_t MAC_timestamp;
    u_int8_t flags;
    u_int8_t dataRate;
    u_int16_t channelfrequency;
    u_int16_t channelType;
    int ssiSignal:8;
    int ssiNoise:8;
};
#endif
struct wi_frame {
    u_int16_t fc;
    u_int16_t wi_duration;
    u_int8_t wi_add1[6];
    u_int8_t wi_add2[6];
    u_int8_t wi_add3[6];
    u_int16_t wi_sequenceControl;
    // u_int8_t wi_add4[6];
    //unsigned int qosControl:2;
    //unsigned int frameBody[23124];
};

void processPacket(u_char *arg, const struct pcap_pkthdr* pkthdr, const u_char* packet)
{
    int i= 0, *counter = (int *) arg;
    struct ieee80211_radiotap_header *rh =(struct ieee80211_radiotap_header *)packet;
    struct wi_frame *fr= (struct wi_frame *)(packet + rh->it_len);
    u_char *ptr;
    //printf("Frame Type: %d",fr->wi_fC->type);
    printf("Packet count: %d\n", ++(*counter));
    printf("Received Packet Size: %d\n", pkthdr->len);
    if(rh->it_version != NULL)
    {
      printf("Radiotap Version: %d\n",rh->it_version);
    }
    if(rh->it_pad!=NULL)
    {
      printf("Radiotap Pad: %d\n",rh->it_pad);
    }
    if(rh->it_len != NULL)
    {
        printf("Radiotap Length: %d\n",rh->it_len);
    }
    if(rh->it_present != NULL)
    {
        printf("Radiotap Present: %c\n",rh->it_present);
    }
    if(rh->MAC_timestamp != NULL)
    {
        printf("Radiotap Timestamp: %u\n",rh->MAC_timestamp);
    }

    if(rh->dataRate != NULL)
    {
        printf("Radiotap Data Rate: %u\n",rh->dataRate);
    }
    if(rh->channelfrequency != NULL)
    {
        printf("Radiotap Channel Freq: %u\n",rh->channelfrequency);
    }
    if(rh->channelType != NULL)
    {
    printf("Radiotap Channel Type: %06x\n",rh->channelType);
    }
    if(rh->ssiSignal != NULL)
    {
        printf("Radiotap SSI signal: %d\n",rh->ssiSignal);
    } 
    if(rh->ssiNoise != NULL)
    {
        printf("Radiotap SSI Noise: %d\n",rh->ssiNoise);
    } 

ptr = fr->wi_add1;
int k= 6;
printf("Destination Address:");
do{
    printf("%s%X",(k==6)?" ":":",*ptr++);
}
while(--k>0);
printf("\n");

ptr = fr->wi_add2;
k=0;
printf("Source Address:");
do{
    printf("%s%X",(k==6)?" ":":",*ptr++);
}while(--k>0);
printf("\n");

ptr = fr->wi_add3;
k=0;
do{
    printf("%s%X",(k==6)?" ":":",*ptr++);
}
while(--k>0);
printf("\n");
/* for(int j = 0; j < 23124;j++)
 {
 if(fr->frameBody[j]!= NULL)
 {
 printf("%x",fr->frameBody[j]);
 }
 }
 */
for (i = 0;i<pkthdr->len;i++)
{

    if(isprint(packet[i +rh->it_len]))
    {
        printf("%c",packet[i + rh->it_len]);    
    }

    else{printf(".");}



    //print newline after each section of the packet
    if((i%16 ==0 && i!=0) ||(i==pkthdr->len-1))
    {
        printf("\n");
    }

}
return;
}
int main(int argc, char** argv)
{

int count = 0;
pcap_t* descr = NULL;
char errbuf[PCAP_ERRBUF_SIZE], *device = NULL;
struct bpf_program fp;
char filter[]="wlan broadcast";
const u_char* packet;
memset(errbuf,0,PCAP_ERRBUF_SIZE);
device = argv[1];

if(device == NULL)
{
    fprintf(stdout,"Supply a device name ");
}

descr = pcap_create(device,errbuf);
pcap_set_rfmon(descr,1);
pcap_set_promisc(descr,1);
pcap_set_snaplen(descr,30);
pcap_set_timeout(descr,10000);

pcap_activate(descr);
int dl =pcap_datalink(descr);
printf("The Data Link type is %s",pcap_datalink_val_to_name(dl));
//pcap_dispatch(descr,MAXBYTES2CAPTURE,1,512,errbuf);
//Open device in promiscuous mode
//descr = pcap_open_live(device,MAXBYTES2CAPTURE,1,512,errbuf);

/* if(pcap_compile(descr,&fp,filter,0,PCAP_NETMASK_UNKNOWN)==-1)
 {
 fprintf(stderr,"Error compiling filter\n");
 exit(1);
 }

 if(pcap_setfilter(descr,&fp)==-1)
 {
 fprintf(stderr,"Error setting filter\n");
 exit(1);
 }
 */
pcap_loop(descr,0, processPacket, (u_char *) &count);

return 0;
}