Linux c++ error: undefined reference to 'dlopen'

Question

I work in Linux with C++ (Eclipse), and want to use a library. Eclipse shows me an error:

undefined reference to 'dlopen' 

Do you know a solution?

Here is my code:

#include <stdlib.h>
#include <stdio.h>
#include <dlfcn.h>

int main(int argc, char **argv) {
    void *handle;
    double (*desk)(char*);
    char *error;

    handle = dlopen ("/lib/CEDD_LIB.so.6", RTLD_LAZY);
    if (!handle) {
        fputs (dlerror(), stderr);
        exit(1);
    }

    desk= dlsym(handle, "Apply");

    if ((error = dlerror()) != NULL)  {
        fputs(error, stderr);
        exit(1);
    }

    dlclose(handle);
}

Answer 1

You have to link against libdl, add

-ldl

to your linker options

Answer 2

@Masci is correct, but in case you're using C (and the gcc compiler) take in account that this doesn't work:

gcc -ldl dlopentest.c

But this does:

gcc dlopentest.c -ldl

Took me a bit to figure out...

Answer 3

this doesn't work:

gcc -ldl dlopentest.c

But this does:

gcc dlopentest.c -ldl

That's one annoying "feature" for sure

I was struggling with it when writing heredoc syntax and found some interesting facts. With CC=Clang, this works:

$CC -ldl -x c -o app.exe - << EOF
#include <dlfcn.h>
#include <stdio.h>
int main(void)
{
  if(dlopen("libc.so.6", RTLD_LAZY | RTLD_GLOBAL))
    printf("libc.so.6 loading succeeded\n");
  else
    printf("libc.so.6 loading failed\n");
  return 0;
}
EOF

./app.exe

as well as all of these:

• $CC -ldl -x c -o app.exe - << EOF
• $CC -x c -ldl -o app.exe - << EOF
• $CC -x c -o app.exe -ldl - << EOF
• $CC -x c -o app.exe - -ldl << EOF

However, with CC=gcc, only the last variant works; -ldl after - (the stdin argument symbol).

Answer 4

I was using CMake to compile my project and I've found the same problem.

The solution described here works like a charm, simply add ${CMAKE_DL_LIBS} to the target_link_libraries() call

Answer 5

The topic is quite old, yet I struggled with the same issue today while compiling cegui 0.7.1 (openVibe prerequisite).

What worked for me was to set: LDFLAGS="-Wl,--no-as-needed" in the Makefile.

I've also tried -ldl for LDFLAGS but to no avail.

Answer 6

you can try to add this

LIBS=-ldl CFLAGS=-fno-strict-aliasing

to the configure options

Answer 7

You needed to do something like this for the makefile:

LDFLAGS='-ldl'
make install

That'll pass the linker flags from make through to the linker. Doesn't matter that the makefile was autogenerated.

Answer 8

I met the same problem even using -ldl.

Besides this option, source files need to be placed before libraries, see undefined reference to `dlopen'.

Answer 9

In order to use dl functions you need to use the -ldl flag for the linker.

how you do it in eclipse ?

Press Project --> Properties --> C/C++ build --> Settings --> GCC C++ Linker -->
Libraries --> in the "Libraries(-l)" box press the "+" sign --> write "dl" (without the quotes)-> press ok --> clean & rebuild your project.

Answer 10

 $gcc -o program program.c -l <library_to_resolve_program.c's_unresolved_symbols>

A good description of why the placement of -l dl matters

But there's also a pretty succinct explanation in the docs From $man gcc

   -llibrary
   -l library
       Search the library named library when linking.  (The second
       alternative with the library as a separate argument is only for POSIX
       compliance and is not recommended.)

       It makes a difference where in the command you write this option; the
       linker searches and processes libraries and object files in the order
       they are specified.  Thus, foo.o -lz bar.o searches library z after
       file foo.o but before bar.o.  If bar.o refers to functions in z,
       those functions may not be loaded.

Answer 11

Try to rebuild openssl (if you are linking with it) with flag no-threads.

Then try to link like this:

target_link_libraries(${project_name} dl pthread crypt m ${CMAKE_DL_LIBS})

Answer 12

In earlier versions(~2.7) of GNU tool chain, glibc did not have direct interface to link loader(dlopen and dlsym functions), so you had to provide -ldl(libdl) at compile time. You don't have to do that anymore with latest glibc version. Just include <dlcfn.h> and you are good to go.

Answer 13

using cmake for me it helped to put -ldl after ssl to the target:

target_link_libraries(ssl_test -WL,--start-group ssl -ldl crypto -WL,--end-group )