Question

consider the code below:

 -module(except).
 -compile(export_all).

 divone(X)->    erlang:error({badnews,erlang:get_stacktrace()}),1/X-1.
 tryreturn(X)->

      try divone(X) of
     Val->{result,2/Val}
    catch
    exit:Reason->{exit,Reason};
    throw:Throw->{throw,Throw};
    error:Error->{error,Error}
 end.

test the code in shell:

 Eshell V5.9.1  (abort with ^G)

 1> c(except).
 {ok,except}
 2> except:tryreturn(10). **%why cant't get stack trace info here?**
 {error,{badnews,[]}}          
 3> except:tryreturn(10). **%why can get here?**
 {error,{badnews,[{except,divone,1,
                     [{file,"except.erl"},{line,4}]},
             {except,tryreturn,1,[{file,"except.erl"},{line,7}]},
             {erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,576}]},
             {shell,exprs,7,[{file,"shell.erl"},{line,668}]},
             {shell,eval_exprs,7,[{file,"shell.erl"},{line,623}]},
             {shell,eval_loop,3,[{file,"shell.erl"},{line,608}]}]}}

Answer 1

If there hasn’t been any exceptions, the stacktrace returned by erlang:backtrace() is empty.

Something more helpful than erlang:backtrace() for you would be something that includes the instruction pointer and the process’s callstack, irrespective of if you’ve caught an exception.

This should be the ticket:

io:format("~s~n", [element(2, process_info(self(), backtrace))]).

(Naturally, self can be freely exchanged with another Pid)