%%-define(debug, ok).
-ifdef(debug).
-define(LOG(X), io:format("pid:~p , {~p,~p}: ~p~n", [self(), ?MODULE, ?LINE, X])).
-else.
-define(LOG(X), true).
-endif.
设置LOG的宏定义，调试只要在代码中加入?LOG(Val)，就可以
特点是，简单，调试清楚，对代码性能的影响小，也是最常用的方法，就不举例说明了
第二种方法，加trace 日志
%trace Mod 所有方法的调用 trace(Mod) -> dbg:tracer(), dbg:p(all, [call]), dbg:tp(Mod, [{‘_‘, [], [{return_trace}]}]); %trace Mod 的Fun方法的调用 trace(Mod) -> dbg:tracer(), dbg:p(all, [call]), dbg:tp(Mod, Fun, [{‘_‘, [], [{return_trace}]}]); %停止trace trace_stop() -> dbg:stop_clear().
特点：对整个模块，或者某些函数进行详细的调试，调试信息比较多，对性能有一段影响。
举例
...... ...... init([Opt]) -> Tab = ets:new(xx, [set]), case opt_find(debug, Opt, false) of %%如果设置了debug，开启debug跟踪 true -> dbg:tracer(), dbg:p(all, [call]), dbg:tp(tt5, [{‘_‘, [], [{return_trace}]}]); _ -> %% Keep silent ok end, {ok, #state{tab = Tab}}. ..... ..... .....
1> c(tt5).
{ok,tt5}
2> tt5:start([{debug, true}]).
{ok,<0.39.0>}
3> tt5:add(name, "wowchina").
(<0.32.0>) call tt5:add(name,"wowchina")
(<0.39.0>) call tt5:handle_call({add,name,"wowchina"},{<0.32.0>,#Ref<0.0.0.104>},{state,16400})
(<0.39.0>) returned from tt5:handle_call/3 -> {reply,true,{state,16400}}
(<0.32.0>) returned from tt5:add/2 -> true
true
4> tt5:find(name).
(<0.32.0>) call tt5:find(name)
(<0.39.0>) call tt5:handle_call({find,name},{<0.32.0>,#Ref<0.0.0.113>},{state,16400})
(<0.39.0>) returned from tt5:handle_call/3 -> {reply,
[{name,"wowchina"}],
{state,16400}}
(<0.32.0>) returned from tt5:find/1 -> [{name,"wowchina"}]
[{name,"wowchina"}]
5>
原文：http://www.cnblogs.com/tudou008/p/5210109.html