Why am I getting an "unresolved external symbol" message?

Question

I am attempting to use IBM's EHLLAPI to interface with their Personal Communicator Terminal Emulator. I have copied their sample code from this page, but it's giving me an error when I try to build it.

1>------ Build started: Project: PCOMAPI, Configuration: Debug Win32 ------
1>  Source.cpp
1>Source.obj : error LNK2019: unresolved external symbol _hllapi@16 referenced in function _main
1>C:\Users\[username]\Documents\Visual Studio 2013\Projects\VPARSAPI\Debug\PCOMAPI.exe : fatal error LNK1120: 1 unresolved externals

I'm not entirely certain what this _hllapi@16 is, and I'm not seeing it in the code. It has been a while since I've worked with C++, so it may be something simple I'm missing. The code is as follows:

#include <stdlib.h>
#include <stdio.h>
#include <windows.h>
#include "hapi_c.h"


int main(char **argv, int argc) {
    int HFunc, HLen, HRc;
    char HBuff[1];
    struct HLDConnectPS ConnBuff;
    // Send Key string for HOME+string+ENTER:
    char SendString[] = "@0Hello World!@E";

    HFunc = HA_RESET_SYSTEM;
    HLen = 0;
    HRc = 0;
    hllapi(&HFunc, HBuff, &HLen, &HRc);
    if (HRc != HARC_SUCCESS) {
        printf("Unable to access EHLLAPI.\n");
        return 1;
    }

    HFunc = HA_CONNECT_PS;
    HLen = sizeof(ConnBuff);
    HRc = 0;
    memset(&ConnBuff, 0x00, sizeof(ConnBuff));
    ConnBuff.stps_shortname = 'A';
    hllapi(&HFunc, (char *)&ConnBuff, &HLen, &HRc);
    switch (HRc) {
    case HARC_SUCCESS:
    case HARC_BUSY:
    case HARC_LOCKED: // All these are OK
        break;
    case HARC_INVALID_PS:
        printf("Host session A does not exist.\n");
        return 1;
    case HARC_UNAVAILABLE:
        printf("Host session A is in use by another EHLLAPI application.\n");
        return 1;
    case HARC_SYSTEM_ERROR:
        printf("System error connecting to session A.\n");
        return 1;
    default:
        printf("Error connecting to session A.\n");
        return 1;
    }

    HFunc = HA_SENDKEY;
    HLen = strlen(SendString);
    HRc = 0;
    hllapi(&HFunc, SendString, &HLen, &HRc);
    switch (HRc) {
    case HARC_SUCCESS:
        break;
    case HARC_BUSY:
    case HARC_LOCKED:
        printf("Send failed, host session locked or busy.\n");
        break;
    default:
        printf("Send failed.\n");
        break;
    }

    HFunc = HA_DISCONNECT_PS;
    HLen = 0;
    HRc = 0;
    hllapi(&HFunc, HBuff, &HLen, &HRc);

    printf("EHLLAPI program ended.\n");
    return 0;
}

My linker flags are:

• /OUT:"C:\Users[username]\Documents\Visual Studio 2013\Projects\VPARSAPI\Debug\PCOMAPI.exe" /MANIFEST /NXCOMPAT
• /PDB:"C:\Users[username]\Documents\Visual Studio
• 2013\Projects\VPARSAPI\Debug\PCOMAPI.pdb" /DYNAMICBASE "kernel32.lib"
• "user32.lib" "gdi32.lib" "winspool.lib" "comdlg32.lib" "advapi32.lib"
• "shell32.lib" "ole32.lib" "oleaut32.lib" "uuid.lib" "odbc32.lib"
• "odbccp32.lib" /DEBUG /MACHINE:X86 /INCREMENTAL
• /PGD:"C:\Users[username]\Documents\Visual Studio2013\Projects\VPARSAPI\Debug\PCOMAPI.pgd" /SUBSYSTEM:CONSOLE
• /MANIFESTUAC:"level='asInvoker' uiAccess='false'"
• /ManifestFile:"Debug\PCOMAPI.exe.intermediate.manifest"
• /ERRORREPORT:PROMPT /NOLOGO /TLBID:1

Answer 1

That is a linker error. You need to pass to the linker the .lib file, the import library, for the EHLLAPI library.

In fact, looking at the documentation, there are a host of .lib files with this library. You'll need to study the documentation carefully to work out which ones you need.

Answer 2

As stated under the section Compiling and Linking you have to include pcscal32.lib for static linking, so the symbols in *hapi_c.h* can be resolved.