Cannot import Global variables from dll into application? - c

Question

I have a DLL
A.dll
This is A.h
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef __cplusplus
#define DLL_EXPORT extern "C" __declspec(dllexport)
#else
#define DLL_EXPORT __declspec(dllexport)
#endif
DLL_EXPORT void function();
DLL_EXPORT char ** ReturnArr;
This is A.c
void function()
{
char *str = "hello";
char *str1 = "how are you?";
ReturnArr = (char **)malloc(sizeof(char*) * 2);
for(;j<2;j++)
{
ReturnArr[j] = (char *) malloc(256);
if(NULL == ReturnArr[j])
break;
}
strcpy(ReturnArr[0],"str");
strcpy(ReturnArr[1],"str1");
}
Now i have Application.c that would use dll
#include <windows.h>
#include <stdio.h>
typedef int (__cdecl *MYPROC)(LPWSTR);
_declspec(dllimport) char ** ReturnArr;
int main( void )
{
HINSTANCE hinstLib;
MYPROC ProcAdd;
int a = 0;
BOOL fFreeResult, fRunTimeLinkSuccess = FALSE;
// Get a handle to the DLL module.
hinstLib = LoadLibrary(TEXT("A.dll"));
// If the handle is valid, try to get the function address.
if (hinstLib != NULL)
{
ProcAdd = (MYPROC) GetProcAddress(hinstLib, "function");
// If the function address is valid, call the function.
if (NULL != ProcAdd)
{
fRunTimeLinkSuccess = TRUE;
(ProcAdd) (L"Message sent to the DLL function\n");
printf("%s",Returnarr[0]);
}
fFreeResult = FreeLibrary(hinstLib);
}
// If unable to call the DLL function, use an alternative.
if (! fRunTimeLinkSuccess)
printf("Message printed from executable\n");
return 0;
}
In Visual studio CommonProperties->references:i added A.dll its showing me compiler ##error Error 1 error LNK2001: unresolved external symbol "__declspec(dllimport) char * ##* ReturnArr" (_imp?ReturnArr##3PAPADA)" and "Error 2 fatal error LNK1120: 1 unresolved ##externals"
how can i actually export a Global variable and use in my application,tell me a way how can i actually print ReturnArr as a global variable in my application
thanks

Answer 1

If you want the linker to resolve the ReturnArr imported variable, you have to add A.LIB to the link process. There are several ways to do this.
Add A.LIB to the "additionnal dependecies" in Configuration properties->Linker->Input
Add #pragma comment( lib, "a.lib" ) in Application.c
Make the DLL project a dependency of the EXE project and in the EXE project and set the Configuration properties->linker->General "Link Library dependencies" to yes.
Side notes:
Are you sure yoy want strcpy(ReturnArr[0],"str"); ? Could be
strcpy(ReturnArr[0],str); (without the quote around str)
If you statically link to A, you don't need to LoadLibrary and GetProcAddress.
You could also just supress _declspec(dllimport) char ** ReturnArr;
Your typedef for MYPROC is wrong. The return type of "function" is void, not int
If you want the EXE to know about the ReturnArr, just make it the return value of function!
You should try to explain what exactly you are trying to do