Dynamic Link to DLL with LoadLibrary corrupts control loop
Hello, hope someone could please help me with this, it has been driving me nuts for a while now. It is probably something simple but I can not find it :(
I just want to be able to call a compiled C DLL from another C program. I made a special test project/DLL in order to find out what I am doing wrong.
I am using DEVC++ 4.9.9.2
The test program just loads the DLL and starts looping away, calling the same function(that returns a double) in the DLL a number of times but all of a sudden the loop counter memory space is somehow overwritten and the loop is exited.
When I run the app, here is the output
Code:
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
F:\tmp\test>qtag_test
Loading DLL...TESTDLL.DLL loaded
Mapping functions...Functions mapped
Reading values...
Loop 1 1.234560e+005
Loop 2 1.234560e+005
Loop 3 1.234560e+005
Loop 4 1.234560e+005
Loop 5 1.234560e+005
Loop 6 1.234560e+005
Loop 7 1.234560e+005
Loop 8 1.234560e+005
Loop 1090397184 1.234560e+005
Values read
Unloading DLL...DLL unloaded.
Program terminated normally.
F:\tmp\test>
Here is the DLL.h
Code:
#ifndef _DLL_H_
#define _DLL_H_
#if BUILDING_DLL
# define DLLIMPORT __declspec (dllexport)
#else /* Not BUILDING_DLL */
# define DLLIMPORT __declspec (dllimport)
#endif /* Not BUILDING_DLL */
#include "windows.h"
#include <string.h>
DLLIMPORT double WINAPI ReadRealValue (LPSTR lpzTagName);
#endif /* _DLL_H_ */
and the DLL.C
Code:
#include "TESTDLL.h"
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
BOOL APIENTRY DllMain (HINSTANCE hInst /* Library instance handle. */ ,
DWORD reason /* Reason this function is being called. */ ,
LPVOID reserved /* Not used. */ )
{
switch (reason)
{
case DLL_PROCESS_ATTACH:
break;
case DLL_PROCESS_DETACH:
break;
case DLL_THREAD_ATTACH:
break;
case DLL_THREAD_DETACH:
break;
}
/* Returns TRUE on success, FALSE on failure */
return TRUE;
}
DLLIMPORT double WINAPI ReadRealValue (LPSTR lpzTagName)
{
double dValue=0;
dValue = 123456;;
return dValue;
}
And finally the test program
Code:
#include <windows.h>
#include <stdio.h>
typedef double (*MYPROC)(LPSTR);
int main(VOID)
{
HINSTANCE hinstLib;
MYPROC ProcAdd=NULL;
BOOL fFreeResult, fRunTimeLinkSuccess = FALSE;
int uDummy;
long lngLoop;
double dvalue;
dvalue=0;
// Get a handle to the DLL module.
printf("Loading DLL...");
hinstLib = LoadLibrary(TEXT("TESTDLL.dll"));
printf("TESTDLL.DLL loaded\n");
// If the handle is valid, try to get the function address.
if (hinstLib != NULL)
{
printf("Mapping functions...");
ProcAdd = (MYPROC) GetProcAddress(hinstLib, "ReadRealValue");
printf("Functions mapped\n");
// If the function address is valid, call the function.
if (NULL != ProcAdd)
{
fRunTimeLinkSuccess = TRUE;
printf("Reading values...\n");
// loop and read
lngLoop=0;
for (lngLoop=1;lngLoop<200;lngLoop++)
{
dvalue=ProcAdd("APP_REAL_1_B");
printf("Loop %i %e\n",lngLoop,dvalue);
sleep(0);
}
printf("Values read\n");
}
// Free the DLL module.
printf("Unloading DLL...");
fFreeResult = FreeLibrary(hinstLib);
printf("DLL unloaded.\n");
}
// If unable to call the DLL function, use an alternative.
if (! fRunTimeLinkSuccess)
{
printf("Failure loading dll.\n");
}
printf("Program terminated normally.\n");
return 0;
}
What am I doing wrong here?
Thankful for help,
/R
