How to mix C++ and C correctly

Question

I am having some problems with this: I need to write a C wrapper for a C++ library. Say I have 3 files:

• wrapper.h

  typedef struct Foo Foo;
  Fo         
  
  
          

Answer 1

You are creating a shared object named a.out, then another shared object named libbindings.so that ostensibly links to a.out but references nothing from it. Now if a set of input files doesn't have any undefined symbols, no libraries are searched or added to the output. So libbindings.so is essentially an empty library. Verify:

 % nm a.out | grep create_foo
 00000000000006bc T create_foo
 % nm libbindings.so | grep create_foo
 %

If you have several source files, you should build an object file from each source (use -c compilation flag), (then optionally combine the objects into a static library --- skip this step if you are not releasing static libraries) then build a shared object from previously built objects:

  clang++ -c -fPIC foo.cpp
  clang++ -c -fPIC bar.cpp
  clang++ -shared -o libfoobar.so foo.o bar.o

If you only have one source, or very few source files you can easily compile together, you can build the shared library in one step:

  clang++ -std=c++14 wrapper.cpp somethingelse.cpp -shared -fPIC -o libbindings.so

This is not recommended for large projects.