Odd "undefined reference" error

Question

So I'm trying to make a really simple abstraction library on top of the Windows API using C. I made a simple Makefile and when I try to make the project using Msys, I get this:

winapi.o: In function `get_client_pid':
(long path)/winapi.c:13: undefined reference to `GetExtendedTcpTable'
(long path)/winapi.c:31: undefined reference to `GetExtendedTcpTable'
collect2.exe: error: ld returned 1 exit status
make: *** [lib] Error 1

and get_client_pid() is defined in winapi.c as

#include <stdint.h>
#include <stdio.h>
#include <windows.h>
#include <Iphlpapi.h>

#define true 1
#define false 0


    uint32_t get_client_pid()
    {
        MIB_TCPTABLE_OWNER_PID *tcpTable;
        PDWORD tableSize;
        DWORD ret = GetExtendedTcpTable(tcpTable, 
                                        tableSize, 
                                        true, 
                                        2, 
                                        TCP_TABLE_OWNER_PID_ALL,
                                        0);

        if (ret == NO_ERROR) {
            printf("ERROR get_client_pid: No error with table size at 0?\n");
            return 0;
        }
        if (ret != ERROR_INSUFFICIENT_BUFFER) {
            printf("ERROR get_client_pid: No insufficient buffer with table size at 0?\n");
            return 0;
        }
        printf("TABLE SIZE %d\n", *tableSize);
        tcpTable = malloc(*tableSize);

        ret = GetExtendedTcpTable(  tcpTable,
                                    tableSize, 
                                    true,
                                    2,
                                    TCP_TABLE_OWNER_PID_ALL,
                                    0);

        if (ret != NO_ERROR) {
            printf("ERROR get_client_pid: GetExtendedTcpTable error: %d\n", ret);
            free(tcpTable);
            return 0;
        }

        int i;
        for (i = 0; i < tcpTable->dwNumEntries; i++) {
            MIB_TCPROW_OWNER_PID row = tcpTable->table[i];
            if (row.dwRemotePort == 0x208 && row.dwRemoteAddr == 0x100007F) {
                printf("FOUND PROCESS: %d\n", row.dwOwningPid);
                free(tcpTable);
                return row.dwOwningPid;
            }
        }

        free(tcpTable);
        return 0;
    }

As this is a linker error, I'll add my makefile:

current_dir = $(shell pwd)

all: test

test: lib
    gcc -c -g tests.c
    gcc -o tests.exe tests.o -L$(current_dir) -lwinapi

lib:
    gcc -c -g winapi.c
    gcc -shared -o winapi.dll winapi.o -lIphlpapi -luser32

clean:
    rm *.o

I have to say that I tried every possible place to insert "-lIphlpapi" in case the linking was somehow in the wrong order but that didn't help.

Answer 1

MinGW defines WINVER as 0x400 (Windows NT) in windef.h, and this means that some newer features of Windows will not link.

#ifndef WINVER
#define WINVER 0x0400
/*
 * If you need Win32 API features newer the Win95 and WinNT then you must
 * define WINVER before including windows.h or any other method of including
 * the windef.h header.
 */
#endif

So you need to define WINVER yourself to the version of Windows you are targeting before including any Windows headers.

Use one of the following definitions:

#define WINVER 0x0500 // Windows 2000
#define WINVER 0x0501 // Windows XP
#define WINVER 0x0502 // Windows Server 2003
#define WINVER 0x0600 // Windows Vista, Windows Server 2008
#define WINVER 0x0601 // Windows 7
#define WINVER 0x0602 // Windows 8
#define WINVER 0x0603 // Windows 8.1
#define WINVER 0x0A00 // Windows 10