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Old 04-27-2009, 11:06 AM   #1
Registered: Feb 2009
Posts: 52

Rep: Reputation: 15
Linux + Code Blocks + Shared Library + my Implementation = Not Working!

I have been trying to create shared objects since about midnight, and am at the point where I need some help.

I have a .c and .h file that I am creating a .so for, I seem to be able to compile the files fine, but the second I go and try to link them in to a .c console app I get unrefereced errors.

I started by using just a text editor and the terminal, and go the creation of the .so down with a simple hello world app, and even linked it in nicely.

But now I am trying to do it with my own program and seem not to be able to get it down.

Currently I am using code blocks, I create a new project of type shared library, i use the gcc compiler, and i make a c file that looks like this
int SampleAddInt(int i1, int i2)
    return i1 + i2;
An .h file that looks like this:
int SampleAddInt(int i1, int i2);
which when compiled gives me a file named

From here I create a new project of type console
I create a main.cpp file where I:

#include <iostream>
#include "main.h" //.h file shown above
using namespace std;
int main()
    cout << "Hello world!" << endl;
    int returnval = SampleAddInt(4, 10); //function in so
    return 0;
and I get the error
||warning:, needed by, not found (try using -rpath or -rpath-link)|
obj/Debug/main.o||In function `main':|
/main.cpp|9|undefined reference to `SampleAddInt(int, int)'|
||=== Build finished: 1 errors, 3 warnings ===|
I right click on the project, go to build properties, linker, and add a relative path to the .so file

I tried this on my own in the terminal as well and seem to have no luck, when using the terminal I am following a few different tutorials
the one I am specificly using is
$ldconfig -v -n .
$ ln -sf
$ gcc -o client client.c -L. -lprint
Now for this code, I place the so in the same directory, it worked just fine for there example, but not for the code above

What is it that I am doing wrong, why can I only get a simple hello world to work, but not this simple .so with the one function to work?

Thank you

[root@GMFedora Test1]# gcc -fPIC -c main.c
[root@GMFedora Test1]# ld -shared -soname -o -lc main.o
[root@GMFedora Test1]# ldconfig -v -n .
.: -> -> (changed)
[root@GMFedora Test1]# ln -sf
[root@GMFedora Test1]# export LD_LIBRARY_PATH=.:$LD_LIBRARY_PATH
[root@GMFedora Test1]# gcc -o client client.c -L. -lprint
/usr/bin/ld: cannot find -lprint
collect2: ld returned 1 exit status
[root@GMFedora Test1]# gcc -o client client.c -L.
/tmp/ccFvAAvm.o: In function `main':
client.c:(.text+0x21): undefined reference to `SampleAddInt'
collect2: ld returned 1 exit status
[root@GMFedora Test1]#

Last edited by morty346; 04-27-2009 at 11:24 AM.
Old 04-27-2009, 05:21 PM   #2
Registered: Feb 2002
Location: Grenoble
Distribution: Debian
Posts: 9,681

Rep: Reputation: 218Reputation: 218Reputation: 218
You're mixing C and C++ code. This will not work that easily. C++ mangles function names, so probably it's searching for something completely different than SampleAddInt which is in the library. That's why you get an error. You need to modify the header file:
#ifdef __cplusplus
extern "C" {
int SampleAddInt(int i1, int i2);
#ifdef __cplusplus
Note also that you need to compile the program (not the library, in this case it's your choice) using g++, not gcc!


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