A trival example of linux dynamic loading (dlopen())

What is this?

A small example of linux dlopen() command. Changed from the one in dlopen manual. Differences:

1. Load a newly defined library instead of the system library.
2. Use cmake.

Dynamic loading?

See Wiki: Dynamic loading.

Notice that here the main program is not linked with the library my_lib. Instead, it find and load it with its name at run time, then find a function in the library with the name and call it.

I put the executable and the library together and even build them together just for convenience. In practice, the program may not have any knowledge of the library at compile time. This is usually used to implement the extension system.

Usage

Have it run

git clone https://github.com/fd3kyt/dlopen_example.git
cd dlopen_example
# wrap with parentheses to keep current working directory
(mkdir -p build && cd build && cmake .. && make)
LD_LIBRARY_PATH="./build/src/" ./build/src/main

Read the files

• src/
  • main.cc : example code of using dlopen().
  • my_lib.cc : how to write a library for dynamic loading?
    • Write C functions (extern "C" if c++)
  • CMakeLists.txt
    • link ${CMAKE_DL_LIBS} to the executable
    • create a shared library in cmake : the SHARED flag in add_library