Linux dlopen undefined reference to

How to fix C++ error “undefined reference to `dlopen’”

You need to link the dl (dynamic linker) library to your executable. When running gcc manually, use the -ldl option, for example:

add_executable(myexe main.cpp) target_link_libraries(myexe dl)

Full error log example:

/usr/bin/ld: /home/uli/.conan/data/openssl/1.1.1k/_/_/package/6af9cc7cb931c5ad942174fd7838eb655717c709/lib/libcrypto.a(dso_dlfcn.o): in function `dlfcn_globallookup': dso_dlfcn.c:(.text+0x17): undefined reference to `dlopen' /usr/bin/ld: dso_dlfcn.c:(.text+0x2a): undefined reference to `dlsym' /usr/bin/ld: dso_dlfcn.c:(.text+0x35): undefined reference to `dlclose' /usr/bin/ld: /home/uli/.conan/data/openssl/1.1.1k/_/_/package/6af9cc7cb931c5ad942174fd7838eb655717c709/lib/libcrypto.a(dso_dlfcn.o): in function `dlfcn_bind_func': dso_dlfcn.c:(.text+0x1b7): undefined reference to `dlsym' /usr/bin/ld: dso_dlfcn.c:(.text+0x282): undefined reference to `dlerror' /usr/bin/ld: /home/uli/.conan/data/openssl/1.1.1k/_/_/package/6af9cc7cb931c5ad942174fd7838eb655717c709/lib/libcrypto.a(dso_dlfcn.o): in function `dlfcn_load': dso_dlfcn.c:(.text+0x2f5): undefined reference to `dlopen' /usr/bin/ld: dso_dlfcn.c:(.text+0x369): undefined reference to `dlclose' /usr/bin/ld: dso_dlfcn.c:(.text+0x3a5): undefined reference to `dlerror' /usr/bin/ld: /home/uli/.conan/data/openssl/1.1.1k/_/_/package/6af9cc7cb931c5ad942174fd7838eb655717c709/lib/libcrypto.a(dso_dlfcn.o): in function `dlfcn_pathbyaddr': dso_dlfcn.c:(.text+0x466): undefined reference to `dladdr' /usr/bin/ld: dso_dlfcn.c:(.text+0x4d7): undefined reference to `dlerror' /usr/bin/ld: /home/uli/.conan/data/openssl/1.1.1k/_/_/package/6af9cc7cb931c5ad942174fd7838eb655717c709/lib/libcrypto.a(dso_dlfcn.o): in function `dlfcn_unload': dso_dlfcn.c:(.text+0x6b8): undefined reference to `dlclose'

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How to fix linux c++ error: undefined reference to ‘dlopen’?

The error «undefined reference to ‘dlopen'» in C++ on Linux systems is a linking error that occurs when the program is trying to use the dynamic loading function ‘dlopen’, but the linker can’t find its definition in any of the libraries specified during the compilation and linking process.

Method 1: Link with the Dynamic Linking Library

To fix the Linux C++ error «undefined reference to ‘dlopen'», you can link with the Dynamic Linking Library. Here are the steps:

void* handle = dlopen("libmylib.so", RTLD_LAZY);

if (!handle)  std::cerr  <"Cannot load library: "  <dlerror()  <'\n'; return 1; >

myFunc = (void (*)()) dlsym(handle, "myFunction");

if (!myFunc)  std::cerr  <"Cannot load symbol 'myFunction': "  <dlerror()  <'\n'; dlclose(handle); return 1; >

Here is the complete example code:

#include #include int main()  // Declare function pointer void (*myFunc)(); // Load library void* handle = dlopen("libmylib.so", RTLD_LAZY); if (!handle)  std::cerr  <"Cannot load library: "  <dlerror()  <'\n'; return 1; > // Get function address myFunc = (void (*)()) dlsym(handle, "myFunction"); if (!myFunc)  std::cerr  <"Cannot load symbol 'myFunction': "  <dlerror()  <'\n'; dlclose(handle); return 1; > // Call function myFunc(); // Close library dlclose(handle); return 0; >

This should fix the Linux C++ error «undefined reference to ‘dlopen'» when using Dynamic Linking Library.

Method 2: Use -ldl Compiler Option

To fix the Linux c++ error «undefined reference to ‘dlopen'», you can use the -ldl compiler option. This option links the program with the dynamic linker library, which provides the dlopen function.

Here are the steps to use the -ldl compiler option:

1. Open your terminal and navigate to the directory where your C++ file is located.
2. Compile your C++ file with the -ldl option using the following command:

g++ your_program.cpp -o your_program -ldl

#include dlfcn.h> #include iostream> typedef int (*my_func)(int, int); int main() < void* handle = dlopen("./my_library.so", RTLD_LAZY); if (!handle) < std::cerr my_func func = reinterpret_castmy_func>(dlsym(handle, "my_function")); if (!func) < std::cerr int result = func(2, 3); std::cout

Method 3: Check for Compatibility Issues with the Library

One possible solution to fix the Linux c++ error "undefined reference to 'dlopen'" is to check for compatibility issues with the library. This can be done by verifying that the library is correctly installed and linked, and that the correct version of the library is being used.

Here is an example of how to check for compatibility issues with the library using the C++ code:

#include #include int main()  void* libHandle = dlopen("libexample.so", RTLD_LAZY); if (!libHandle)  std::cerr  <"Error loading library: "  <dlerror()  ::endl; return 1; > // use the library dlclose(libHandle); return 0; >

This code uses the dlopen() function from the dlfcn.h library to load the shared library libexample.so at runtime. The RTLD_LAZY flag indicates that symbol resolution should be deferred until the symbols are actually used.

If the library cannot be loaded, dlopen() returns NULL and the error message can be obtained using the dlerror() function.

Once the library is loaded, its symbols can be accessed using the dlsym() function, which takes the library handle and the symbol name as arguments.

Finally, the dlclose() function is used to release the library handle and unload the library from memory.

By following these steps, you can check for compatibility issues with the library and resolve the "undefined reference to 'dlopen'" error in your C++ program.

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Segmentation fault and undefined reference to `dlopen'

I try to load libraries dynamically in c++. I follow this tutorial. My folder structure is like this :

├── main.cpp ├── testLib.cpp ├── testLib.h ├── testLib.so └── testVir.h 

#include #include #include #include "testVir.h" using namespace std; int main() < void *handle; handle = dlopen("./testLib.so", RTLD_NOW); if (!handle) < printf("The error is %s", dlerror()); >typedef TestVir* create_t(); typedef void destroy_t(TestVir*); create_t* creat=(create_t*)dlsym(handle,"create"); destroy_t* destroy=(destroy_t*)dlsym(handle,"destroy"); if (!creat) < coutif (!destroy) < coutTestVir* tst = creat(); tst->init(); destroy(tst); return 0 ; > 

#include #include "testVir.h" #include "testLib.h" using namespace std; void TestLib::init() < cout//Define functions with C symbols (create/destroy TestLib instance). extern "C" TestLib* create() < return new TestLib; >extern "C" void destroy(TestLib* Tl)

#ifndef TESTLIB_H #define TESTLIB_H class TestLib < public: void init(); >; #endif 

#ifndef TESTVIR_H #define TESTVIR_H class TestVir < public: virtual void init()=0; >; #endif 

I get my testLib.so using this command g++ -shared -fPIC testLib.cpp -o testLib.so , this works fine, but when i try to compile my main with g++ -ldl main.cpp -o test i get this errors :

/tmp/ccFoBr2X.o: In function `main': main.cpp:(.text+0x14): undefined reference to `dlopen' main.cpp:(.text+0x24): undefined reference to `dlerror' main.cpp:(.text+0x47): undefined reference to `dlsym' main.cpp:(.text+0x5c): undefined reference to `dlsym' main.cpp:(.text+0x6c): undefined reference to `dlerror' main.cpp:(.text+0x95): undefined reference to `dlerror' collect2: error: ld returned 1 exit status 

G++ version ( from g++ --version ) :
g++ (Ubuntu 4.8.4-2ubuntu1~14.04.1) 4.8.4 I don't know what is going one, I would need some resources in learning how this works. EDIT 1 I solved the problem by using this command to compile my main. g++ main.cpp -ldl -o test . Found this fix in this answer . But now when i try to run ./test i get Segmentation fault . And it seems to be at this line tst->init(); but the pointer looks valid. EDIT 2 Following this tutorial i get the same error, Segmentation fault . If you have good tutorials or documentations it would really help.

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

I've had this error in a situation different to presented above. The fix was to reorder the -l flags. I had to put -dl after (in my case) -ssl and the error went away.

12 Answers 12

You have to link against libdl, add

I have run into the same problem. I added the compiler flag under Project>Properties>C/C++Build>Settings>(My Linker)>Miscellaneous in the Linker flags text field. It did nothing.

Ha, ok, for anyone else that has this problem, use the above path, except go to Libraries rather than Miscellaneous and add the 'dl'

This answer helped. For anyone who wants to find the location of libdl.so, just go to the root directory and type locate libdl.so

MirroredFate's answer worked for me as well. I don't understand why, though; every other library I've ever had to link worked when placed in Miscellaneous.

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

Took me a bit to figure out.

I've found that the order of the options matters too. On a project using sqlite3, I have to put -ldl (and -lpthread) after -lsqlite3. Don't know what that is, I'm sure the answer is there if I would just RTFM.

Holy crap, that's it! I would never have guessed that putting the options first (which makes more sense to me) doesn't work, while putting them after does. Thank you, @knocte!

for anyone who is wondering why this is, its because ld reads the libraries left to right then notes any undefined symbols, filling them in when a different library gives them. the problem being it doesn't check for undefined symbols in the files before the one it is linking

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 - #include 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 

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

I encounter such problem too. But I don't know why gcc dlopentest.c -ldl works whereas gcc -ldl dlopentest.c does not. How do you think about it?

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 $ to the target_link_libraries() call

Thanks! This helped me as well. But only after I changed my compiler to clang SET(CMAKE_CXX_COMPILER /usr/bin/clang++) . With /usr/bin/c++ on my Ubuntu it was not working. (see also vulcan raven's answer)

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.

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

Using the LIBS variable worked for me to get configure to put -ldl in the right place on the command line.

You needed to do something like this for the makefile:

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

I met the same problem even using -ldl .

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

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

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.

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. 

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Linux c++ error: undefined reference to ‘dlopen’

When working with dynamic libraries in Linux c++, you may encounter an error that says “undefined reference to ‘dlopen'”. This error occurs when the linker is unable to find the required symbols for the `dlopen` function. In this guide, we’ll go through the steps to resolve this error with code examples.

Step 1: Include the dl library

The `dlopen` function is defined in the `dl` library, so you need to include it in your code. To do this, add the following line at the beginning of your source file:

Step 2: Link against the dl library

In addition to including the `dl` library, you also need to link against it during the compilation process. This can be done by adding the `-ldl` flag to your compile command. For example:

g++ -o myprogram myprogram.cpp -ldl 

Step 3: Use dlopen in your code

With the `dl` library included and linked against, you can now use the `dlopen` function in your code. Here is an example:

#include #include int main() < void* handle = dlopen("libmylibrary.so", RTLD_LAZY); if (!handle) < std::cerr // use the library. dlclose(handle); return 0; > 

In this example, we’re using the `dlopen` function to load a dynamic library called `libmylibrary.so`. The `RTLD_LAZY` flag specifies that symbol resolution should be performed when a symbol is first referenced by the program.

Conclusion

By including the `dl` library, linking against it, and using the `dlopen` function correctly, you can resolve the “undefined reference to ‘dlopen'” error in Linux c++. With these steps, you can successfully work with dynamic libraries in your code.

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