Linux c++ error: undefined reference to 'dlopen'
C++LinuxEclipseC++ Problem Overview
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);
}
C++ Solutions
Solution 1 - C++
You have to link against libdl, add
> -ldl
to your linker options
Solution 2 - C++
@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...
Solution 3 - C++
> 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).
Solution 4 - C++
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
Solution 5 - C++
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.
Solution 6 - C++
you can try to add this
LIBS=-ldl CFLAGS=-fno-strict-aliasing
to the configure options
Solution 7 - C++
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.
Solution 8 - C++
I met the same problem even using -ldl
.
Besides this option, source files need to be placed before libraries, see https://stackoverflow.com/questions/6183899/undefined-reference-to-dlopen.
Solution 9 - C++
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.
Solution 10 - C++
$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 $man gcc
> -llibrary -l library Search the library named library when linking. (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.)
It makes a difference where in the command you write this option; the
linker searches and processes libraries and object files in the order
they are specified. Thus, foo.o -lz bar.o searches library z after
file foo.o but before bar.o. If bar.o refers to functions in z,
those functions may not be loaded.
Solution 11 - C++
Try to rebuild openssl (if you are linking with it) with flag no-threads
.
Then try to link like this:
target_link_libraries(${project_name} dl pthread crypt m ${CMAKE_DL_LIBS})
Solution 12 - C++
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