Calling extern functions in a c library

Hi I am new to JNI and I am trying to use an existing c library that I have in a java application.
I have written a c function which is called from java class, this works fine, the problem is when i try to call functions located in my c library from this function the code wont compile, giving a linker error. Specifically it wont compile the functions marked as being extern in the header file.
I tried removing extern, but had the same error, I am not a c programmer.
Any help would be really appreciated

Hi,
I doubt you will get a response since this thread is 7 years old. You are better off looking up the documentation for your compiler as this is not really a JNI question.
With gcc you would use -L<lib_dir> -l<lib>
Cheers,
Shane

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How to call external functions without a .DLL (just using a .H and .LIB file)?

Hello everyone,
actually I'm facing little difficulties on how to get an external function getting called from within CVI (Version 2009).
I was supplied with a .H file and a .LIB file to call an external function from within my CVI project. The .H file looks like this:
void exportedFunction(double *parameter);
As far as I know, the external function was written with MS Visual C++ 6.
So I tried to statically link to the extern al function like this:
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When building I get an unresolved external function call error from CVI so this seems not to be working.
I made some searches around and got up with two possible issues. Maybe one of you can help me get a bit further and get things working.
1) The "real" function code is located in the DLL file which was not delivered to me. Or is there a way to get things done (call external functions) just with a .H and a .LIB file (without any .DLL file included)?
2) The external function does not export according to "C-Style" rules. The function signature in the .H file shows no things like
extern "C" __declspec(dllexport) void __stdcall ...
Or maybe it's a combination of both issues (missing .DLL + wrong export style of function)?
I guess I could get around the wrong export style of the function when I manage to write a wrapper around the original function that actually uses C-Style exporting. But I guess I need the .DLL file for this try as well.
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Best regards,
Bernd
Solved!
Go to Solution.

There is no need for the dllexport stuff. There is also the option for a static library without any DLL. But the 'extern "C"' is essential, because it forces the C++ compiler, which was probably used to compile the library , to use C calling convention.
If you can't ask the provider of the library to provide a version which was compiled using C calling convention the way to go is to write a wrapper with VC++6 around that library which reexports the functions using C calling convertion. Something like
extern "C" type0 myfunc1(type1 arg1, ...) {
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IN general, Windows loads dll's automatically when required by a program. The only requirement is that the dll be on the "search path". Two places you can guarantee will be searched are the directory from which the program was loaded, and the win32 directory.
There are ways to PREVENT this automatic loading, and instead put it completely under program control. But why would you want to do that?

When calling a function in a shared library, are parameters copied locally?

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Lars Melander
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Go to Solution.

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Call external function from SQL query

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Yes it is possible.
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Here you go.
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Calling external C-functions in DLLs with struct as parameters

Hi all PL/SQL Gurus !
Is it possible to call external functions in a DLL written in C
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Hi,
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Can Any one tell me what is the step in calling a function from a *.lib file in Labview application

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Regards
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patil wrote:
When it is possible in Lab Windows, why calling a function from a static library is prohibited?
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LabWindows is not the same as LabVIEW. LabVIEW cannot call .lib files. LIB files are intermediary products and you need to use a wrapper DLL that's compatible with the object format of the .lib file. It's as simple as that. LabWindows creates C application and from that perspective is no different than a regular C
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Using visual studio I wrote the following code test javascript communication with external C/C++ libraries:
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What would be the correct procedure to call a function inside a DLL?

FRM-40734 when calling external DLL Function from Forms 6

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Error when calling external DLL function.

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Calling a function in an external actionscript

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Call multiple functions from same dll with call library function

hi,
i am working on a project in wich we need to make a UI to read out a sensor network.
the UI should be usable in any project, but every node needs a different piece of code depending on the type of sensor with wich it is equipt.
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nazarim wrote:
ok so there is no (easy and ubderstandable) way for me to dynamicly change wich function i want to call from a certain DLL.
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a division of Test & Measurement Solutions

PDA: How does the VI in the "Calling External Code (Inline C Method)" example link to the called functions?

The PDA module provides an example of calling external code via an inline C
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Donovan B wrote:
Hi Dan,
It looks like there is an OSVERSIONINFO struct and GetVersionEx function available in the coredll.lib for the application to call on a PDA running Windows Mobile 5.0. On both operating systems, it looks like the GetVersionEx function is defined in winbase.h, so I am not sure if there is some kind of linking between the two or if the header file is automatically included when building the executable or not. Let me do some more research and I'll let you know.
The information for the function on Windows Mobile can be found here.
Message Edited by Donovan B on 12-19-2007 06:33 PM
While the API functions are mostly the same for Windows Mobile and normal Windows the actual implementation and compilation is obviously not and there is no need for that. Windwos Mobile is typically (not sure if there are other versions at all) ARM based, while the desktop version is x86 based. A huge difference.
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Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

Calling extern functions in a c library

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