bar.c

__declspec(dllexport) int bunny = 273;
__declspec(dllexport) int rabbit() { return 273; }

command

> cl /c bar.c ; link /dll bar.obj ; cl /c foo.c ; link foo.obj bar.lib
Microsoft (R) C/C++ Optimizing Compiler Version 19.00.24213.1 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

bar.c
Microsoft (R) Incremental Linker Version 14.00.24213.1
Copyright (C) Microsoft Corporation.  All rights reserved.

   Creating library bar.lib and object bar.exp
Microsoft (R) C/C++ Optimizing Compiler Version 19.00.24213.1 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

foo.c
Microsoft (R) Incremental Linker Version 14.00.24213.1
Copyright (C) Microsoft Corporation.  All rights reserved.

foo.obj : error LNK2019: unresolved external symbol bunny referenced in function main
foo.exe : fatal error LNK1120: 1 unresolved externals

foo.c

#include <stdio.h>
extern int bunny;
__declspec(dllimport) int rabbit();
int main() {
    printf("%d", bunny);
    printf("%d", rabbit());
}