Why am I getting an "unresolved external symbol" message? - c++

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.