code:
#include <cstdlib>
#include <iostream>
#include <windows.h>
using namespace std;
void calldll();
int main(int argc, char *argv[])
{
calldll();
system("PAUSE");
return EXIT_SUCCESS;
}
void calldll()
{
HINSTANCE LoadMe;
LoadMe = LoadLibrary("Trans_ATL.dll");
if(LoadMe!=0)
cout<<"loaded successfully\n";
else
cout<<"loading error\n";
/* get pointer to the functions in the dll*/
FARPROC function01 = GetProcAddress(LoadMe,"EnableLastCharTashkeel");
FARPROC function02 = GetProcAddress(LoadMe,"EnableEmphaticLAM_RAA");
FARPROC function03 = GetProcAddress(LoadMe,"SetText");
FARPROC function04 = GetProcAddress(LoadMe,"GetResult");
typedef void (__stdcall * pICFUNC01)(bool);
typedef void (__stdcall * pICFUNC02)(bool);
typedef bool (__stdcall * pICFUNC03)(string);
typedef string (__stdcall * pICFUNC04)(string);
pICFUNC01 EnableLastCharTashkeel_function;
EnableLastCharTashkeel_function = pICFUNC01(function01);
pICFUNC02 EnableEmphaticLAM_RAA_function;
EnableEmphaticLAM_RAA_function = pICFUNC02(function02);
pICFUNC03 SetText_function;
SetText_function = pICFUNC03(function03);
pICFUNC04 GetResult_function;
GetResult_function = pICFUNC04(function04);
EnableLastCharTashkeel_function(true);
EnableEmphaticLAM_RAA_function(true);
FreeLibrary(LoadMe);
}
in this code i call a dll it load successfully but when i try to use any function it compile without any errors but at the line
EnableLastCharTashkeel_function(true); (first call for a function)
it froozes and give me the following
Unhandled exception at 0x00000000 in test_trans_new.exe: 0xC0000005: Access violation reading location 0x00000000.
i guess that this becuse the function pointer point to NULL but i don't know how to fix it
i use visual c++ 2010
thanks in advance
thank you for all your replies which are realy helpfull but the problem still ocurrs but i approximately know the reason if i correct the problem is that the functions i try to access are of type COM so any idea about using this type
thanks in advance
FARPROC function01 = GetProcAddress(LoadMe,"EnableLastCharTashkeel");
That's a guaranteed NULL. Calling it does go kaboom, you didn't check if the function succeeded. The exported function is not named "EnableLastCharTashkeel". A more likely string is "?EnableLastCharTashkeel##YAX_N#Z". That's the name of the function after the C++ compiler mangled it, a trick to support overloaded functions.
You can declare the function extern "C", that suppresses name mangling and makes the function name "_EnableLastCharTashkeel". Note the leading underscore, used by the 32-bit compiler to mark that the function uses the __cdecl calling convention. To be sure, run Dumpbin.exe /exports on your DLL from the Visual Studio Command Prompt, it shows the exported names.
It's most likely 0 because the symbol you were trying to find in the DLL wasn't found, which would suggest that (a) it's either not there or (b) there might be a typo in the function name or (c) the function name might be mangled because it's being exported as a decorated name. This happens quite a lot in C++...
Unless the library exporting those four functions is under your control, use dumpbin /EXPORTS and have a look at the correct spelling of the symbols.
Related
This is my exported function in dll1
extern"C" __declspec(dllexport) int FUN1(char* p){
return p[0];
}
I am calling this FUN1 from other project.Below is the code
#include
#include
using namespace std;
typedef int (*MYFUN1)(char*);
int main()
{
HMODULE hMod = LoadLibrary ("C:\\Users\\admin\\Documents\\Visual Studio 2010\\Projects\\CalledFun\\Debug\\CalledFun.exe");
if(hMod != NULL)
{
MYFUN1 pCtor = (MYFUN1) GetProcAddress (hMod, "FUN1");
int a = pCtor("calling a value") ;
cout<<a;
}
}
If I remove the extern "C" from dll1 then that function address is returning as NULL when calling GetProcAddress in dll2. Since both are written in c++ I thought name mangling will not effect this.I thought if we use c and c++ libraries combinely then only we need to mention extern "C" ,Can anyone help me to get out of this confusion
Thanks in advance
You need to disable name mangling because you are using Windows API like LoadLibrary to which you provide function name. Windows API an LoadLibrary in particular know nothing about your compiler name mangling, so you need to turn it off.
Okay so I'm coming dangerously close to a repost here but my situation is a little bit different than the numerous other posters about this function. I am interfacing with a DLL that was written way back in the day and all I have is the file. I don't have a .lib file so I'm using the LoadLibrary and GetProcessAddress functions. I followed the tutorial on the MSDN website to get the basic structure. the DLL is located in the project folder. it compiles. at run time, I am getting a numerical value for "hinstLib" so I'm assuming the DLL was found. I am getting a null value for "ProcAdd" variable. Other posters had there issues resolved by putting extern C in the DLL functions but I don't really have that option. not to mention, to my knowledge this DLL was written in plain C. I do have an interface document and am quite sure I have the function name correct (replaced with a generic example for these purposes). I honestly didn't run anything past the ProcAdd assignment because it came out NULL. Any thoughts as to why this is giving me a 0 value for the function assignment would be great appreciated. Note: unfortunately due to various reasons I can't upload the DLL.
#include <iostream>
#include "stdafx.h"
#include "Windows.h"
#include <stdio.h>
typedef int(__cdecl *MYPROC)(LPWSTR);
using namespace std;
int main()
{
HINSTANCE hinstLib;
MYPROC ProcAdd;
BOOL fFreeResult, fRunTimeLinkSuccess = FALSE;
hinstLib = LoadLibrary(TEXT("dllName.dll"));
if (hinstLib != NULL)
{
ProcAdd = (MYPROC) GetProcAddress(hinstLib, "funcName");
// If the function address is valid, call the function.
if (NULL != ProcAdd)
{
fRunTimeLinkSuccess = TRUE;
//(ProcAdd) (L"Message sent to the DLL function\n");
}
// Free the DLL module.
fFreeResult = FreeLibrary(hinstLib);
}
// If unable to call the DLL function, use an alternative.
if (! fRunTimeLinkSuccess)
printf("Message printed from executable\n");
return 0;
}
Compilers usually mangle function names, then a function named funcName may appear inside the DLL with a name funcName#16 , for example... It depends on calling convention and are important for a function to be called properly. For __cdecl calling convention you probably need _funcName :-) .
I created a DLL file (helloWorld.dll):
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#define DLL_FUNC extern "C" __declspec(dllexport)
DLL_FUNC int __stdcall Hello() {
MessageBox(HWND_DESKTOP, "Hello, world", "MEssage", MB_OK);
return 0;
}
After that I created a cpp where I would like to call (useDLL.cpp)
#include <windows.h>
#include <stdio.h>
int main () {
typedef void (*pfunc)();
HINSTANCE hdll = LoadLibrary("HelloWorld.dll");
pfunc Hello;
Hello = (pfunc)GetProcAddress(hdll, "hello");
Hello();
return 0;
}
How can I call the Hello() function?
The code in the question contains a number of errors:
LoadLibrary returns HMODULE and not HINSTANCE
The function pointer has the wrong return value and an incorrect calling convention.
Function names are case sensitive and you must account for name decoration.
You did no error checking at all. Your code probably fails on the call to GetProcAddress, returns NULL and then bombs when you try to call the function at NULL.
So you need something like this:
typedef int (__stdcall *HelloProc)();
....
HMODULE hdll = LoadLibrary("HelloWorld.dll");
if (hdll == NULL)
// handle error
HelloProc Hello = (HelloProc)GetProcAddress(hdll, "_Hello#0");
if (Hello == NULL)
// handle error
int retval = Hello();
The function name is decorated because you used __stdcall. If you had used __cdecl, or a .def file, then there would have been no decoration. I'm assuming MSVC decoration. It seems that decoration differs with your compiler, mingw, and the function is named "Hello#0".
Frankly it's much easier to do it with a .lib file instead of calling LoadLibrary and GetProcAddress. If you can, I'd switch to that way now.
You need to specifically search and find specific functions you are lookins for, check out this link:
Calling functions in a DLL from C++
I want to use pjsipDll.dll in a c++ code. I got this dll from one of the sites, I only know how to build the code to obtain the dll file. So I did that and now I've the pjsipDll.dll file with me. I want to use certain functions in the DLL in my code(C++)
I tried the following code. << I haven't made/added any dll or .h file to the project, there is only the following CPP file>>
#include <iostream>
using namespace std;
int CallMyDLL(void)
{
/* get handle to dll */
HINSTANCE hGetProcIDDLL = LoadLibrary("G:\\July\\9.0\\pjsipdll\\Lib\\pjsipDll.dll");
/* get pointer to the function in the dll*/
FARPROC lpfnGetProcessID = GetProcAddress(HMODULE (hGetProcIDDLL),"dll_makeCall");
/*
Define the Function in the DLL for reuse. This is just prototyping the dll's function.
A mock of it. Use "stdcall" for maximum compatibility.
*/
typedef int (__stdcall * pICFUNC)(int, char *);
pICFUNC MyFunction;
MyFunction = pICFUNC(lpfnGetProcessID);
/* The actual call to the function contained in the dll */
int intMyReturnVal = MyFunction(5,"hello");
/* Release the Dll */
FreeLibrary(hGetProcIDDLL);
/* The return val from the dll */
returnintMyReturnVal;
}
void main()
{
cout<<"Hello World";
CallMyDLL();
getchar();
}
I learnt this way from some site, to use the function from a DLL.
The problem is, I get an ERROR:
error C2065: 'HINSTANCE' : undeclared identifier g:\july\9.0\pjproject-0.9.0\myproject\importerprojet\importerprojet\mycpp.cpp 9 importerProjet
Can anyone help me out with this. Or atleast point me to the post if this query is already addressed.
Thanks for your help,
Vinu.
You need to #include <windows.h>
Hello guys: I've loaded my DLL in my project but whenever I use the GetProcAddress function. it returns NULL! what should I do?
I use this function ( double GetNumber(double x) ) in "MYDLL.dll"
Here is a code which I used:
typedef double (*LPGETNUMBER)(double Nbr);
HINSTANCE hDLL = NULL;
LPGETNUMBER lpGetNumber;
hDLL = LoadLibrary(L"MYDLL.DLL");
lpGetNumber = (LPGETNUMBER)GetProcAddress((HMODULE)hDLL, "GetNumber");
Checking return codes and calling GetLastError() will set you free. You should be checking return codes twice here. You are actually checking return codes zero times.
hDLL = LoadLibrary(L"MYDLL.DLL");
Check hDLL. Is it NULL? If so, call GetLastError() to find out why. It may be as simple as "File Not Found".
lpGetNumber = (LPGETNUMBER)GetProcAddress((HMODULE)hDLL, "GetNumber");
If lpGetNumber is NULL, call GetLastError(). It will tell you why the proc address could not be found. There are a few likely scenarios:
There is no exported function named GetNumber
There is an exported function named GetNumber, but it is not marked extern "c", resulting in name mangling.
hDLL isn't a valid library handle.
If it turns out to be #1 above, you need to export the functions by decorating the declaration with __declspec(dllexport) like this:
MyFile.h
__declspec(dllexport) int GetNumber();
If it turns out to be #2 above, you need to do this:
extern "C"
{
__declspec(dllexport) int GetNumber();
};
You might want to check if your GetNumber function is exported as an __stdcall function.
If so, try GetProcAddress(hDLL, "_GetNumber#N");, where N is the total number of bytes of GetNumber's argument list. For example, if your function signature is int GetNumber(int a, double b), its real name in DLL will be _GetNumber#12.
Reference: __stdcall
Most probably LoadLibrary() failed. You just can't see that because apparently you are not checking what it is returning:
If the function fails, the return value is NULL. To get extended error information, call GetLastError.
EDIT:
We don't know how you are exporting the function on the DLL code, but this thread explains a couple of reasons on why GetProcAddress fails.