Roslaunch cannot open shared object file: No such file or directory

Question

I'm having problems with opening a shared library when using roslaunch.

I have a ROS package with a c++ script containing the line:

handle = dlopen("./rk4.so", RTLD_LAZY);

This shared library resides inside my ROS package. I managed to build the package with catking build, having in my CMakeLists.txt the lines

add_library(RK4 SHARED IMPORTED)
set_target_properties(RK4 PROPERTIES IMPORTED_LOCATION ${CMAKE_CURRENT_SOURCE_DIR}/src/SharedLibs/rk4.so)

target_link_libraries(simulator_node
  RK4
  ${CMAKE_DL_LIBS}
  ${catkin_LIBRARIES} 
)

The problem is when I try to run my executable. Since the library is not in a folder where libraries usually are, I added the path to that folder to LD_LIBRARY_PATH and exported it. However I don't understand why I don't get the error in the title only when I use rosrun while I'm inside the exact folder in which the library is. My issue is that I want to launch that node with a launch file, but using roslaunch I get the error in the title anyway, even if I run it from inside the folder of that library.

Answer 1

I think the most portable way of doing so is to supply dlopen with the full path to the shared library file by using ros::package::getPath("your_package_name") as follows (and not modifying LD_LIBRARY_PATH!). This way you can easily get your package up and running on another computer!

• Modify your node to load the shared library using the absolute path to the shared library by using the function ros::package::getPath from the ros/package.h header:

  std::string const library_path = ros::package::getPath("your_package") + "/relative/path/to/libyourlib.so";
  auto* handle = ::dlopen(library_path.c_str(), RTLD_LAZY);
  

  This for example would be a minimal working example for a node your_node :

  #include <cstdlib>
  #include <iostream>
  #include <string>
  
  #include <dlfcn.h>
  
  #include <ros/ros.h>
  #include <ros/package.h>
  
  int main (int argc, char** argv) {
    ros::init(argc, argv, "your_node");
    ros::NodeHandle n;
  
    std::string const package_path = ros::package::getPath("your_package");
    std::string const library_path = package_path + "/src/libyourlib.so";
    auto* handle = ::dlopen(library_path.c_str(), RTLD_LAZY);
  
    if (!handle) {
      std::cerr << "Error: could not load shared library!" << std::endl;
    } else {
      std::cout << "Library successfully loaded!" << std::endl;
    }
    return EXIT_SUCCESS;
  }
  

• Modify your CMakeLists.txt to include the roslib library which contains the ros::package::getPath function:

  find_package(catkin REQUIRED COMPONENTS
    roscpp
    roslib
  )
  
  include_directories(
    ${catkin_INCLUDE_DIRS}
  )
  
  add_executable(your_node src/your_node.cpp)
  target_link_libraries(your_node ${catkin_LIBRARIES} ${CMAKE_DL_LIBS})