CODEWITHSUNDEEP
c++cvisual-studio-2013header-filesmsdn
Phoenix
Phoenix

Reputation: 4646

Inspecting C Header Files Further

I am learning networking in c by looking at the code of a working packet sniffer within Microsoft Visual Basic 2013.

Below is code that creates a pointer to a hostent structure, obtains the localhost hostname, and loads it into the hostent structure called local.

struct hostent *local;
gethostname(hostname, sizeof(hostname))
local = gethostbyname(hostname);

The next part enables the address to be printed in dotted decimal notation.

for (i = 0; local->h_addr_list[i] != 0; ++i)
{
    memcpy(&addr, local->h_addr_list[i], sizeof(struct in_addr));
    printf("  Interface Number : %d Address : %s\n",i,inet_ntoa(addr));
}

Now, I want to understand how all this works and more . . .

Say I want to understand inet_ntoa(), I right-click and choose Go To Definition or Go To Declaration and it sends me to WinSock2.h that shows:

inet_ntoa(
    __in struct in_addr in
);

This appears to be show me the parameter but not the workings of the function or the return value. This means I have to refer to the MSDN to understand what is happening every time.

My question is: Where is the code to read what is happening so I don't have to use the docs?

E.g. where is the inet_ntoa function contents?

Upvotes: 0

Views: 96

Answers (1)

LiGhTx117
LiGhTx117

Reputation: 218

Here you are:

#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h>

/* The interface of this function is completely stupid, it requires a
   static buffer.  We relax this a bit in that we allow one buffer for
   each thread.  */

static __thread char buffer[18];

char *inet_ntoa (struct in_addr in)
{
   unsigned char *bytes = (unsigned char *) &in;
   __snprintf (buffer, sizeof (buffer), "%d.%d.%d.%d",
               bytes[0], bytes[1], bytes[2], bytes[3]);

  return buffer;
}

Taken from inet_ntoa.c, glibc 2.23

Remember that the glibc is open source, so if you want to explore a bit and learn what's going in under the hood, don't hesitate and download it !

Regards

Upvotes: 3

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