Thread: Extract IP from HTML of webpage

Hello, I am just beginning on sockets in C and I need to make a program that finds my external IP.

Through a bit of research on this forum I decided to make the program request the source of www.whatsmyip.com and find the IP.

I have got the source:

Code:

char* file_contents = GetInternetFile(TEXT("http://www.whatsmyipaddress.com/"), 100000, &sz);

But please can you tell me how I would extract the IP after the text "your ip is".

Would I be using scanf?

Or is there a more direct way of doing this?

Cheers

Well assuming GetInternalFile stores all the html in the file_contents buffer you could use strstr() to find the occurence of your ip is, and take the ip address after that.

Cheers for quick reply.

Ok so I get all contents starting at "Your IP Address is":

printf(strstr(file_contents, "Your IP Address is"));

Now what function would I use to put the IP address into a variable.

And what parameters could I put on the strstr() function to make it start at the ip.

I am thinking maybe if it starts with the ip i can read the 1st 12 characters.

Thanks

Thats exactly what I was looking for. Cheers

strstr finds the first occurrence of the requested string in the provided string, and returns a pointer to the beginning of it.

Now, you need to set the pointer to where the actual string you want is. You could then copy out your data by walking the string until you hit a character that's not a number or a period (dot).

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

int main()
{
   // Want to get the needle
   const char * const haystack = "This is a string with a needle in it.";
   const char * const search = "a string with a";
   const char *p = strstr(haystack, search);
   if (p)
   {
      // p now points to "a string with a"
      // Increment p past the end of the needle
      p += strlen(search);

      while (*p && isspace(*p)) ++p; // skip any spaces

      if (*p == '\0')
         return 1;

      const char *start_of_needle = p;

      while (*p && !isspace(*p)) ++p; // find the next space

      char *needle = malloc(p - start_of_needle + 1);
      if (!needle)
         return 1;
      strncpy(needle, start_of_needle, p - start_of_needle);
      needle[p - start_of_needle] = '\0';

      printf("Needle: %s\n", needle);
      free(needle);
   }

   return 0;
}

I am only beginning C but that still helped. Useful bit of code.

Okay so used the automation page/directory in the latter ip website.

As I have a separate .c file for finding the ip I need to pass it to the file that actually uses the ip in a format that can be used like this - to construct a socket:

Obviously needs changing a bit.

Code:

    memset(&echoServAddr, 0, sizeof(echoServAddr));   /* Zero out structure */
    echoServAddr.sin_family = AF_INET;                /* Internet address family */
    echoServAddr.sin_addr.s_addr = htonl(INADDR_ANY); /* Any incoming interface */
    echoServAddr.sin_port = htons(echoServPort);      /* Local port */

Problem is I get a compile warning - and dont shoot me if this is a lame question, im new to c:
get_ip.c [Warning] return makes integer from pointer without a cast

Code:

char get_ip(void)
{
	size_t sz;
	
    char* file_contents = GetInternetFile(TEXT("http://www.whatismyip.com/automation/n09230945.asp"), 100, &sz);

	return file_contents;
}

Should be:

Code:

char* get_ip(void)

That did the trick.

My last question now is, how would I get the internal IP address of my machine?

Can I have a few hints on how to use the:

gethostbyname() on the value gethostname() returns.

method please.

Dont worry about last question - have researched more and found the answer.

Why not just have your own web server running on a machine built just to collect IPs and extract the IPs from your log files? What exactly are you trying to do, John?