11.4 Debugging support

When debugging a CLN application with GNU gdb, two facilities are available from the library:

• The library does type checks, range checks, consistency checks at many places. When one of these fails, an exception of a type derived from runtime_exception is thrown. When an exception is cought, the stack has already been unwound, so it is may not be possible to tell at which point the exception was thrown. For debugging, it is best to set up a catchpoint at the event of throwning a C++ exception:

  (gdb) catch throw
  

  When this catchpoint is hit, look at the stack’s backtrace:

  (gdb) where
  

  When control over the type of exception is required, it may be possible to set a breakpoint at the g++ runtime library function __raise_exception. Refer to the documentation of GNU gdb for details.

• The debugger’s normal print command doesn’t know about CLN’s types and therefore prints mostly useless hexadecimal addresses. CLN offers a function cl_print, callable from the debugger, for printing number objects. In order to get this function, you have to define the macro ‘CL_DEBUG’ and then include all the header files for which you want cl_print debugging support. For example:

  #define CL_DEBUG
  #include <cln/string.h>
  

  Now, if you have in your program a variable cl_string s, and inspect it under gdb, the output may look like this:

  (gdb) print s
  $7 = {<cl_gcpointer> = { = {pointer = 0x8055b60, heappointer = 0x8055b60,
    word = 134568800}}, }
  (gdb) call cl_print(s)
  (cl_string) ""
  $8 = 134568800
  

  Note that the output of cl_print goes to the program’s error output, not to gdb’s standard output.

  Note, however, that the above facility does not work with all CLN types, only with number objects and similar. Therefore CLN offers a member function debug_print() on all CLN types. The same macro ‘CL_DEBUG’ is needed for this member function to be implemented. Under gdb, you call it like this:

  (gdb) print s
  $7 = {<cl_gcpointer> = { = {pointer = 0x8055b60, heappointer = 0x8055b60,
    word = 134568800}}, }
  (gdb) call s.debug_print()
  (cl_string) ""
  (gdb) define cprint
  >call ($1).debug_print()
  >end
  (gdb) cprint s
  (cl_string) ""
  

  Unfortunately, this feature does not seem to work under all circumstances.

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