How get information from LIBPCAP? - c++

Question

I need to get information about internet package and I was trying with the following code but I don't have experience with C++.
I executed this code from this tutorial http://yuba.stanford.edu/~casado/pcap/section1.html
#include <stdio.h>
#include <stdlib.h>
#include <pcap.h> /* GIMME a libpcap plz! */
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int main(int argc, char **argv)
{
char *dev; /* name of the device to use */
char *net; /* dot notation of the network address */
char *mask;/* dot notation of the network mask */
int ret; /* return code */
char errbuf[PCAP_ERRBUF_SIZE];
bpf_u_int32 netp; /* ip */
bpf_u_int32 maskp;/* subnet mask */
struct in_addr addr;
/* ask pcap to find a valid device for use to sniff on */
dev = pcap_lookupdev(errbuf);
/* error checking */
if(dev == NULL)
{
printf("%s\n",errbuf);
exit(1);
}
/* print out device name */
printf("DEV: %s\n",dev);
/* ask pcap for the network address and mask of the device */
ret = pcap_lookupnet(dev,&netp,&maskp,errbuf);
if(ret == -1)
{
printf("%s\n",errbuf);
exit(1);
}
/* get the network address in a human readable form */
addr.s_addr = netp;
net = inet_ntoa(addr);
if(net == NULL)/* thanks Scott :-P */
{
perror("inet_ntoa");
exit(1);
}
printf("NET: %s\n",net);
/* do the same as above for the device's mask */
addr.s_addr = maskp;
mask = inet_ntoa(addr);
if(mask == NULL)
{
perror("inet_ntoa");
exit(1);
}
printf("MASK: %s\n",mask);
return 0;
}
When I execute this code, I get a file a.out but I cannot open the file, why? How can i pass my information to .csv?

Answer 1

I don't have experience with C++
Although the code may compile using a C++ compiler it looks more like C code. The name of the file, ldev.c, and the compiler used also says that it's a C program.
When I execute this code, I get a file a.out but I cannot open the file, why?
The last step in the tutorial tells you how to compile the program, not how to execute it:
gcc ldev.c -lpcap
That step produces a.out which is the program you are supposed to execute.
To actually execute the program, run the command:
./a.out
Then, if everything works, the output should be something similar to:
DEV: eth0
NET: 192.168.12.0
MASK: 255.255.255.0

Answer 2

Writing to a .csv file is not very different from the basic writing to any other file.
We need to open the file using the library
#include <fstream>
Then we create our file to write to
std::ofstream outputFile;
we open it using
outputFile.open("random.csv");
and start writing using commas as separators
outputFile << "a,b,c,\n";
outputFile << mask << "\n"; // in your case
Then don't forget to close it!
outputFile.close();