title: gdb how to set breakpoint in dynamic library opened by dlopen
body: <p>Afternoon,everbody.
  I have an application 'test' compiled by main.c . A dynamic liabrary 'libtest.so' which is compiled by test.cpp with '-g'. In main.c I invoke the 'libtest.so' with 'dlopen' . And now I want to  set a breakpoint in test.cpp ,but the gdb never hit it. I do as follow:</p>
  
  <p><em>gdb ./test -d /home/lcl/test</em></p>
  
  <p><em>break test.cpp:35</em></p>
  
  <p><em>run</em></p>
  
  <p>can anybody give me some tips ,thanks!</p>