/usr/bin/C++ not compile as gcc with Shared library

Question

I try to work on shared library.

In detail, I following this link: http://www.cprogramming.com/tutorial/shared-libraries-linux-gcc.html.

Everything ok with this command:

$ gcc -L/home/user/foo -Wl,-rpath=/home/user/foo -Wall -o test main.c -lfoo
$ ./test

But when i change from gcc to /usr/bin/c++, ANd change commands to:

$ /usr/bin/c++ -L/home/user/foo -Wl,-rpath=/home/user/foo -Wall -o test2 main.c -lfoo
/tmp/ccpEHbNV.o: In function `main':
main.c:(.text+0x16): undefined reference to `foo()'
collect2: error: ld returned 1 exit status

It can't find the method foo in my libfoo.so.

I also try by another way with -rdynamic, It also work well with gcc:

gcc -rdynamic ./libfoo.so -Wl,-rpath=/home/user/foo -Wall -o test main.c -lfoo

But It also have the same error with /usr/bin/c++.

Please show me how to make it work with /usr/bin/c++.

Thank a lot.

Don't mix and match compilers, the name mangling won't match. Compile both the lib and main.c with either gcc, or g++, not both. You could also wrap the declarations with extern "C" and appropriate compiler guards if you really do need to use the lib in both C and C++. — user657267
– user657267, Commented Dec 14, 2016 at 7:25
/usr/bin/c++ is a standard name for C++ compiler. It can be any compiler on your system. For example, on my system it is the same as g++. You can check it with ls -l /usr/bin/{g,c}++. On some systems c++ is a symlink to g++. On my system it is just a copy of g++ (checked with md5sum /usr/bin/{g,c}++). So it is impossible to answer unless you tell us which compiler is disguised under /usr/bin/c++. By the way, the commands work with g++, so it is unlikely that your c++ is g++. — Ruslan Osmanov
– Ruslan Osmanov, Commented Dec 14, 2016 at 7:50
C and C++ are different languages. If you compile the library with a C compiler and your code with a C++ compiler, you need to ensure that the library's functions are declared with C linkage in C++. — molbdnilo
– molbdnilo, Commented Dec 14, 2016 at 8:02
I don't understand. /usr/bin/c++ is compiler in C++ right. If I change anything from C to Cpp. I also meet with the same problem. — phuong
– phuong, Commented Dec 14, 2016 at 8:17

e.jahandar · Accepted Answer · 2016-12-14 08:11:21Z

2

As others said, this is because different symbol naming between C and C++ compiled libraries, As C++ have overloaded functions the naming for each symbol should include type of arguments in symbol name or something which identifies the actual function or class method based on its arguments. Unlike C++, C doesn't have this issue, because of no function overloading and its standard ABI. if you want mix C/C++ files you have to compile all the C & C++ codes with g++ and also add extern C keyword to definition of C codes

#ifdef __cplusplus
extern "C" {
#endif

// your C definitions (only function definitions) goes here

#ifdef __cplusplus
}
#endif

answered Dec 14, 2016 at 8:11

e.jahandar

1,76313 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

shiv · Accepted Answer · 2016-12-14 07:26:03Z

1

The problem is coming probably because of name mangling of C++. /usr/bin/c++ ends up as /usr/bin/g++. gcc is a C compiler while g++ is a C++ compiler. You need to compile your library libfoo.so with g++ and then try to link. It should work.

answered Dec 14, 2016 at 7:26

shiv

1,9721 gold badge17 silver badges24 bronze badges

2 Comments

Ruslan Osmanov Over a year ago

"gcc is a C compiler while g++ is a C++ compiler" - GCC is C and C++ compiler. Read NAME section from the man page.

shiv Over a year ago

I know gcc means GNU Compiler Collection. Historically, gcc is the command for C language.

strikr · Accepted Answer · 2016-12-14 08:43:41Z

-1

What is the version of gcc and c++ you are using ?

Ideally within the same compiler tool-chain family there should be no error.

In fact, i wrote the code, compiled and executed the same example without any issues.

Please note the version of gcc/c++ i am using.

gcc (GCC) 6.2.1 20160830
g++ (GCC) 6.2.1 20160830

i wrote a shell script file to execute the commands

strace c++ -c -Wall -Werror -fpic foo.c
strace c++ -shared -o libfoo.so foo.o
strace c++ -L. -Wall -o test main.c -lfoo

and collected the strace output of the compilation and linking. Please see the link below http://pastebin.com/nJpQuCfS

Hope this helps.

answered Dec 14, 2016 at 8:43

strikr

12 bronze badges

Collectives™ on Stack Overflow

/usr/bin/C++ not compile as gcc with Shared library

3 Answers 3

Comments

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related