Getting TCP state list

Sample code

The following sample code shows how to use GetTcpTable().

#include <stdio.h>

#include <winsock2.h>
#include <iphlpapi.h>

int
main()
{
 DWORD i;
 PMIB_TCPTABLE pTcpTable;
 DWORD dwSize = 0;
 DWORD dwRetVal = 0;

 char *addr_ptr;
 unsigned short *port_ptr;

 /* Get size required by GetTcpTable() */
 if (GetTcpTable(NULL, &dwSize, 0) == ERROR_INSUFFICIENT_BUFFER) {
   pTcpTable = (MIB_TCPTABLE *) malloc (dwSize);
 }

 /* Get actual data using GetTcpTable() */
 if ((dwRetVal = GetTcpTable(pTcpTable, &dwSize, 0))
      == NO_ERROR) {
   if (pTcpTable->dwNumEntries > 0) {
     for (i=0; i<pTcpTable->dwNumEntries; i++) {
       addr_ptr = (char *)&pTcpTable->table[i].dwLocalAddr;
       printf("Local Address:  %s\n",
         inet_ntoa(*(struct in_addr *)addr_ptr));

       port_ptr = (unsigned short *)&pTcpTable->table[i].dwLocalPort;
       printf("Local Port:     %ld\n",
         htons(*port_ptr));

       addr_ptr = (char *)&pTcpTable->table[i].dwRemoteAddr;
       printf("Remote Address: %s\n",
         inet_ntoa(*(struct in_addr *)addr_ptr));

       port_ptr = (unsigned short *)&pTcpTable->table[i].dwRemotePort;
       printf("Remote Port:    %ld\n",
         htons(*port_ptr));

       printf("State:          %ld\n", pTcpTable->table[i].dwState);
       printf("\n");
     }
   }
 } else {
   printf("GetTcpTable failed.\n");
   LPVOID lpMsgBuf;
			
   if (FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                     FORMAT_MESSAGE_FROM_SYSTEM | 
                     FORMAT_MESSAGE_IGNORE_INSERTS,
                     NULL,
                     dwRetVal,
                     MAKELANGID(LANG_NEUTRAL,
                                SUBLANG_DEFAULT), //Default language
                     (LPTSTR) &lpMsgBuf,
                     0,
                     NULL ))  {
                       printf("\tError: %s", lpMsgBuf);
   }

   LocalFree( lpMsgBuf );
 }

 return 0;
}

Sample code output

The sample will output an message like the following.

C:> a.exe
Local Address:  0.0.0.0
Local Port:     445
Remote Address: 0.0.0.0
Remote Port:    45262
State:          2

Local Address:  0.0.0.0
Local Port:     135
Remote Address: 0.0.0.0
Remote Port:    2176
State:          2

Local Address:  0.0.0.0
Local Port:     1025
Remote Address: 0.0.0.0
Remote Port:    8332
State:          2

Local Address:  0.0.0.0
Local Port:     1029
Remote Address: 0.0.0.0
Remote Port:    2096
State:          2

Structure used by GetTcpTable()

The following structure is MIB_TCPTABLE that is used by GetIpNetTable().

typedef struct _MIB_TCPROW {
  DWORD dwState;
  DWORD dwLocalAddr;
  DWORD dwLocalPort;
  DWORD dwRemoteAddr;
  DWORD dwRemotePort;
} MIB_TCPROW, *PMIB_TCPROW;

typedef struct _MIB_TCPTABLE {
  DWORD dwNumEntries;
  MIB_TCPROW table[ANY_SIZE];
} MIB_TCPTABLE, *PMIB_TCPTABLE;

MIB_TCPROW

dwState	TCP state.
dwLocalAddr	Local IP address(IPv4).
dwLocalPort	Local TCP port.
dwRemoteAddr	Remote IP address(IPv4).
dwRemotePort	Remote TCP port.

MIB_TCPTABLE

dwNumEntries	Number of TCP entries.
table	TCP entry information is stored as array of MIB_TCPROW. The length of array is shown in dwNumEntries.