GetTcpTable function

The GetTcpTable function retrieves the IPv4 TCP connection table.

Syntax

IPHLPAPI_DLL_LINKAGE ULONG GetTcpTable(
  PMIB_TCPTABLE TcpTable,
  PULONG        SizePointer,
  BOOL          Order
);

Parameters

TcpTable

A pointer to a buffer that receives the TCP connection table as a MIB_TCPTABLE structure.

SizePointer

On input, specifies the size in bytes of the buffer pointed to by the pTcpTable parameter.

On output, if the buffer is not large enough to hold the returned connection table, the function sets this parameter equal to the required buffer size in bytes.

On the Windows SDK released for Windows Vista and later, the data type for this parameter is changed to a PULONG which is equivalent to a PDWORD.

Order

A Boolean value that specifies whether the TCP connection table should be sorted. If this parameter is TRUE, the table is sorted in the order of:

  1. Local IP address
  2. Local port
  3. Remote IP address
  4. Remote port

Return Value

If the function succeeds, the return value is NO_ERROR.

If the function fails, the return value is one of the following error codes.

Return code Description
ERROR_INSUFFICIENT_BUFFER
The buffer pointed to by the pTcpTable parameter is not large enough. The required size is returned in the DWORD variable pointed to by the pdwSize parameter.

This error is also returned if the pTcpTable parameter is NULL.

ERROR_INVALID_PARAMETER
The pdwSize parameter is NULL, or GetTcpTable is unable to write to the memory pointed to by the pdwSize parameter.
ERROR_NOT_SUPPORTED
This function is not supported on the operating system in use on the local system.
STATUS_UNSUCCESSFUL
If you receive this return code then calling the function again is usually enough to clear the issue and get the desired result. This return code can be a consequence of the system being under high load. For example, if the size of the TCP connection table changes by more than 2 additional items 3 consecutive times.
Other
Use FormatMessage to obtain the message string for the returned error.

Remarks

On the Windows SDK released for Windows Vista and later, the return value from the GetTcpTable function is changed to a data type of ULONG which is equivalent to a DWORD.

Examples

The following example retrieves the TCP connection table for IPv4 and prints the state of each connection.

// Need to link with Iphlpapi.lib and Ws2_32.lib
#include <winsock2.h>
#include <ws2tcpip.h>
#include <iphlpapi.h>
#include <stdio.h>

#pragma comment(lib, "iphlpapi.lib")
#pragma comment(lib, "ws2_32.lib")

#define MALLOC(x) HeapAlloc(GetProcessHeap(), 0, (x))
#define FREE(x) HeapFree(GetProcessHeap(), 0, (x))

/* Note: could also use malloc() and free() */

int main()
{

    // Declare and initialize variables
    PMIB_TCPTABLE pTcpTable;
    DWORD dwSize = 0;
    DWORD dwRetVal = 0;

    char szLocalAddr[128];
    char szRemoteAddr[128];

    struct in_addr IpAddr;

    int i;

    pTcpTable = (MIB_TCPTABLE *) MALLOC(sizeof (MIB_TCPTABLE));
    if (pTcpTable == NULL) {
        printf("Error allocating memory\n");
        return 1;
    }

    dwSize = sizeof (MIB_TCPTABLE);
// Make an initial call to GetTcpTable to
// get the necessary size into the dwSize variable
    if ((dwRetVal = GetTcpTable(pTcpTable, &dwSize, TRUE)) ==
        ERROR_INSUFFICIENT_BUFFER) {
        FREE(pTcpTable);
        pTcpTable = (MIB_TCPTABLE *) MALLOC(dwSize);
        if (pTcpTable == NULL) {
            printf("Error allocating memory\n");
            return 1;
        }
    }
// Make a second call to GetTcpTable to get
// the actual data we require
    if ((dwRetVal = GetTcpTable(pTcpTable, &dwSize, TRUE)) == NO_ERROR) {
        printf("\tNumber of entries: %d\n", (int) pTcpTable->dwNumEntries);
        for (i = 0; i < (int) pTcpTable->dwNumEntries; i++) {
            IpAddr.S_un.S_addr = (u_long) pTcpTable->table[i].dwLocalAddr;
            strcpy_s(szLocalAddr, sizeof (szLocalAddr), inet_ntoa(IpAddr));
            IpAddr.S_un.S_addr = (u_long) pTcpTable->table[i].dwRemoteAddr;
            strcpy_s(szRemoteAddr, sizeof (szRemoteAddr), inet_ntoa(IpAddr));

            printf("\n\tTCP[%d] State: %ld - ", i,
                   pTcpTable->table[i].dwState);
            switch (pTcpTable->table[i].dwState) {
            case MIB_TCP_STATE_CLOSED:
                printf("CLOSED\n");
                break;
            case MIB_TCP_STATE_LISTEN:
                printf("LISTEN\n");
                break;
            case MIB_TCP_STATE_SYN_SENT:
                printf("SYN-SENT\n");
                break;
            case MIB_TCP_STATE_SYN_RCVD:
                printf("SYN-RECEIVED\n");
                break;
            case MIB_TCP_STATE_ESTAB:
                printf("ESTABLISHED\n");
                break;
            case MIB_TCP_STATE_FIN_WAIT1:
                printf("FIN-WAIT-1\n");
                break;
            case MIB_TCP_STATE_FIN_WAIT2:
                printf("FIN-WAIT-2 \n");
                break;
            case MIB_TCP_STATE_CLOSE_WAIT:
                printf("CLOSE-WAIT\n");
                break;
            case MIB_TCP_STATE_CLOSING:
                printf("CLOSING\n");
                break;
            case MIB_TCP_STATE_LAST_ACK:
                printf("LAST-ACK\n");
                break;
            case MIB_TCP_STATE_TIME_WAIT:
                printf("TIME-WAIT\n");
                break;
            case MIB_TCP_STATE_DELETE_TCB:
                printf("DELETE-TCB\n");
                break;
            default:
                printf("UNKNOWN dwState value\n");
                break;
            }
            printf("\tTCP[%d] Local Addr: %s\n", i, szLocalAddr);
            printf("\tTCP[%d] Local Port: %d \n", i,
                   ntohs((u_short)pTcpTable->table[i].dwLocalPort));
            printf("\tTCP[%d] Remote Addr: %s\n", i, szRemoteAddr);
            printf("\tTCP[%d] Remote Port: %d\n", i,
                   ntohs((u_short)pTcpTable->table[i].dwRemotePort));
        }
    } else {
        printf("\tGetTcpTable failed with %d\n", dwRetVal);
        FREE(pTcpTable);
        return 1;
    }

    if (pTcpTable != NULL) {
        FREE(pTcpTable);
        pTcpTable = NULL;
    }    

    return 0;    
}


Requirements

   
Minimum supported client Windows 2000 Professional [desktop apps | UWP apps]
Minimum supported server Windows 2000 Server [desktop apps | UWP apps]
Target Platform Windows
Header iphlpapi.h
Library Iphlpapi.lib
DLL Iphlpapi.dll

See Also

GetExtendedTcpTable

GetOwnerModuleFromTcpEntry

GetTcp6Table

GetTcp6Table2

GetTcpStatistics

GetTcpStatisticsEx

GetTcpTable2

MIB_TCPROW

MIB_TCPROW_OWNER_MODULE

MIB_TCPROW_OWNER_PID

MIB_TCPTABLE

MIB_TCPTABLE_OWNER_MODULE

MIB_TCPTABLE_OWNER_PID

SetTcpEntry