DNKROZ DNKROZ - 1 year ago 78
C Question

Unresolved externals (LNK1120)

I am getting the error

fatal error LNK1120: 3 unresolved externals
when compiling my program using Developer CMD Prompt for VS2012.

Each unresolved external symbol has the error:

nickman.obj : error LNK2019: unresolved external symbol _scrninit referenced in function _main
nickman.obj : error LNK2019: unresolved external symbol _scrnnrml referenced in function _main
nickman.obj : error LNK2019: unresolved external symbol _scrneng referenced in function _main

When compiling using GCC i get

cannot find -lpthread
collect2.exe: error: ld returned 1 exit status

I've been told this is also due to unresolved symbols.

I can't seem to see anything wrong with what I've done, but maybe someone else can. I'm guessing there's a problem with the way that I've included the header file

Here is my code:


#include "nickman.h"

void main(void)
unsigned int curr_dat = 0; // The current dat file to use
unsigned char ch = 0; // Key entered at keyboard
unsigned char lastkey = 0; // Last key entered (movement command)

if (scrninit()) {
printf("\nThere was an error initializing the screen.");

if (scrneng(curr_dat)) {
printf("\nThere was an error creating the screen.");

//to leave it on there for us to see



extern int scrninit(); // the screen initialize routine
extern scrnnrml(); // reset screen to normal
extern int scrneng(unsigned curr_dat); // the screen display engine routine


#include "screen.h"

// the screen initialize routine
int scrninit()
_asm {
mov ax,0013h
int 10h
return(0); // for now (no error)

void scrnnrml()
_asm {
mov ax,0003h
int 10h

void display_item(int item_num, int x, int y)
unsigned int postn, temp;

y *= 10;
x *= 10;
postn = y * 320 + x;
temp = item_num * 100;

_asm {
push ds
push es
push si
push di
mov ax,0A000h
mov es,ax
mov si,offset itembitmap
add si,temp
mov di,postn
mov ax,seg itembitmap
mov ds,ax
mov cx,10
push cx
mov cx,05
rep movsw
add di,310
pop cx
loop loop1
pop di
pop si
pop es
pop ds


#include <stdio.h>
#include <stdlib.h>

#include "scrneng.h"

// the screen display engine routine
int scrneng(unsigned curr_dat)
FILE *fp;
int i,j;
unsigned char dat_file[] = "SCRN00.DAT";
unsigned char scrn_grid[21][33];

// open, read in the grid, and close the file
if((fp = fopen(dat_file,"rb"))==NULL) {
printf("\nError opening file");
for (i=1;i<=20;i++) {
for (j=1;j<=32;j++)
scrn_grid[i][j] = fgetc(fp) - 97;
fgetc(fp); // skip CR LF
fgetc(fp); //


return(0); // no error

Sorry for the large code dump, didn't really know what to include and exclude!

Answer Source

You need to specify each file you want to compile on the command line. If you only give the source file that contains main, there's no way for it to know where the other functions live.

For example, if you had screen.c and screen_old.c, both with the same functions but (possibly) different implementations, how would the compiler know which one to use?

You can either compile each one separately to an object file then link the object files:

cl -c nickman.c
cl -c screen.c
cl -c scrneng.c
cl -out:nickman nickman.o screen.o scrneng.o

Or compile and link all at once:

cl -out:nickman nickman.c screen.c scrneng.c
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