Hi
I am creating a shared library on Linux but when i link it with a program it gives undefined reference for a function which is defined in the shared library.

e.g.'
*********Header file function declarattion

<abc.h> int sum(int ,int);

******* definition is in the Shared Library
libabc.so
//definition
#include <abc.h>
int sum(int a,int b)
{
return a+b;

}

************program where i am using that shared library "libabc.so"


#include <abc.h>
int main()
{
int c;
c=sum(10,20);
cout<< c;

}


But when i build it . it gives an error undefined reference to sum(int,int)..
would you please solve my problem.
Thanks and Regard
Harpreet Singh

well we really need to know how your building it and whether the undefined reference is at the compile or link stage, also i see your using cout without iostream?

Hi all
I have solved my problem . Thanx

This is the worst thing you can do in a forum IMO..if you have solved the problem post the answer for future generations pal!!
I am also new to linux development and have the same problem:
my make file follows:
a.out : hello.o
@echo Building Hello World
g++ hello.o -L. -lABC

hello.o : hello.cpp test.c libABC.so
@echo Building Hello
g++ -c hello.cpp -I${COTS_ECLIPSE_BOOST_INCDIR_38} -I/vobs/online/egse_api/egse_api/src/

libABC.so : ABC.o BC.o test.o
@echo Building Library
gcc -shared -Wl,-soname,libABC.so -o libABC.so ABC.o test.o ./BC.o -lc

ABC.o : ABC.cpp
@echo Building ABC
gcc -fPIC -g -c -Wall ABC.cpp

BC.o : BC.cpp
@echo Building ABC
gcc -fPIC -g -c -Wall BC.cpp

test.o : test.c
@echo Building ABC
gcc -fPIC -g -c test.c -o test.o

I've simplified the problem to the same level as the last poster test.c defines one c function sum(int i, int s);

hello.cpp uses that function. you'll notice that that ABC and BC are also in the library the hello.cpp uses those with out error (that is if I remove the sum call I compile fine):

bash-3.2$ make
Building ABC
gcc -fPIC -g -c test.c -o test.o
Building Library
gcc -shared -Wl,-soname,libABC.so -o libABC.so ABC.o test.o ./BC.o -lc
Building Hello
g++ -c hello.cpp -I/usr/include/boost/boost_1_38_0 -I/vobs/online/egse_api/egse_api/src/
Building Hello World
g++ hello.o -L. -lABC /usr/include/boost/boost_1_38_0/stage/lib/libboost_regex-gcc41-mt-1_38.a
hello.o: In function `main':
hello.cpp.text+0x9e): undefined reference to `sum(int, int)'
collect2: ld returned 1 exit status
make: *** [a.out] Error 1

Thanks

Hi -

Superficially, it certainly all *looks* reasonable.

I noticed you're compiling some stuff with C (gcc), and other stuff with C++ (g++). You know that, by default, C++ names are "mangled".

Q: Are you using 'extern "C" {...}' to make sure your external functions are callable by both C and C++? Do you have an extern "C" in your header?

EXAMPLE:PS:
Another "trick" is to use "nm" to verify exactly what symbols are exported from your .so.

I do in my actual code but I did not in my example here I will give it a shot in the simplified example.

... Great that worked thank you!

The code compiles on windows (VC7.1) because I have the extern "C" around the implementation of the source that is:


But did not extern "C" around the header file after adding that to the header it compiles and links fine.
Thanks paulsm4

Cool - glad it worked!

One additional note: you only need the extern "C" in the header, not around the code itself. All you need to do is make sure you #include your header in your source file, before "sum ()".