Using C++ dll in a C application.I want that the C Application will directly call the C++ dll from the specified path and use its functions

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4.00/5 (1 vote)

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Hi All,
I have a problem.
There is a C++ dll which has some functions in it (suppose - Addition of 2 nos.).
and i need to call this addition function from a C application.

Note: I dont want to add/link/refer the source code of C++ dll.
I want that the C Application will directly call the C++ dll from the specified path and use the "Addition()".

Iam using Visual C++ 2008 for all this.
Whatever soluton iam getting over internet, everywhere they tell us to add the reference of the dll project(dll source code)

My requirement is that-
We will only give our C++ dll to the client(who has his C application) and will tell him how he should provide the inputs to the C++ dll and how we are going to give him his output.

Please someone suggest me what i need to do...
What changes i need to do in C++ dll and How we should write the C application such that it can successfully call & use the C++ dll.
Iam a newbie in C/C++ so please help me.

Thanx in advance.
Dinesh kumar dora

Posted 27-Apr-11 0:26am

dinesh_redhawk

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[no name] 27-Apr-11 9:15am

I wrote the code of the app and placed the dll file near the exe file
this is the code snippet of my test application:

#include

int __cdecl sum(int a,int b); // a function from a DLL

int main(VOID)
{
int Ret = 0;
HANDLE hLib = LoadLibrary("TestDLL.dll");
PFARPROC x = GetProcAddress(hLib,"sum");
Ret=x(5,3);
printf("Result (5+3)=%d",Ret);
FreeLibrary(hLib);
return 0;
}
and i got some errors:
error C2065: 'PFARPROC' : undeclared identifier
error C2146: syntax error : missing ';' before identifier 'x'
error C2065: 'x' : undeclared identifier

this is my C++ dll code snippet:
#include

#ifdef __cplusplus // If used by C++ code,
extern "C" { // we need to export the C interface
#endif

__declspec(dllexport) int __cdecl sum(int a1,int b1)
{
int result = 0;
result = a1 + b1;
return result;
}

#ifdef __cplusplus
}
#endif
Successfully built.
NOTE: No header files are included in app as well as in dll.Totally empty project
Please tell me whats wrong in this?

2 solutions

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CPallini · Accepted Answer · 2011-04-27T00:46:00

Solution 1

Please read: "How to mix C and C++"[^] (expecially you need to use the extern "C" construct in your DLL).
If you don't want implicitely link the DLL than you have to use, in the C application, the LoadLibrary function, see "Using Run-Time Dynamic Linking"[^] at MSDN.

Posted 27-Apr-11 0:46am

CPallini

Comments

Joan M 27-Apr-11 7:08am

Good answer, my 5.

CPallini 27-Apr-11 7:44am

Thank you.

Olivier Levrey 27-Apr-11 7:39am

Have my 5 too.

CPallini 27-Apr-11 7:44am

Thanks.

[no name] 27-Apr-11 7:42am

My Five++

CPallini 27-Apr-11 7:44am

Thank you.

Sergey Alexandrovich Kryukov 27-Apr-11 21:34pm

Aha. A 5.
--SA

Debojyoti Majumder · Accepted Answer · 2011-04-27T01:07:00

Solution 2

An example to use DLL files.

HANDLE hLib = LoadLibrary("math.dll");
PFARPROC x = GetProcAddress(hLib,"Addnumbers");
x(23,34);
FreeLibrary(hLib);

Posted 27-Apr-11 1:07am

Debojyoti Majumder

Comments

[no name] 27-Apr-11 7:10am

can we use LoadLibrary() in C code?

LaxmikantYadav 27-Apr-11 7:18am

Yes, It is defined in CRT

Olivier Levrey 27-Apr-11 7:41am

Have a 5 Debojyoti.
I just suggest to cast the returned value of GetProcAddress with the appropriate type.

You need to include windows.h to use LoadLibrary.

[no name] 27-Apr-11 7:50am

ok
iam little bit confused abt all this..
can anyone just post me a sample dll and sample c app
so that i can refer it..plz

[no name] 27-Apr-11 8:33am

I tried your suggestion and iam getting some errors

I wrote the code of the app and placed the dll file near the exe file

this is the code snippet of my test application:
#include "windows.h"

int __cdecl sum(int a,int b); // a function from a DLL
int main(VOID)
{

int Ret = 0;
HANDLE hLib = LoadLibrary("TestDLL.dll");

PFARPROC x = GetProcAddress(hLib,"sum");
Ret=x(5,3);

printf("Result (5+3)=%d",Ret);
FreeLibrary(hLib);
return 0;
}

and i got some errors:
error C2065: 'PFARPROC' : undeclared identifier
error C2146: syntax error : missing ';' before identifier 'x'
error C2065: 'x' : undeclared identifier

this is my C++ dll code snippet:

#include "windows.h"

#ifdef __cplusplus // If used by C++ code,

extern "C" { // we need to export the C interface
#endif

__declspec(dllexport) int __cdecl sum(int a1,int b1)
{ int result = 0;

result = a1 + b1;
return result;
}
#ifdef __cplusplus
}#endif
Successfully built.

NOTE: No header files are included in app as well as in dll.Totally empty project

Please tell me whats wrong in this?
.

Sergey Alexandrovich Kryukov 27-Apr-11 21:31pm

Pure C detected. Correct, my 5.
--SA

Sergey Alexandrovich Kryukov 27-Apr-11 21:33pm

I already voted but noticed... it must be FARPROC not PFARPROC (proc is a pointer by itself...)
Will you fix?
--SA

[no name] 28-Apr-11 0:59am

I also tried replacing PFARPROC to FARPROC...and still i got error - "FARPROC: undeclared identifier"