### zeosutt's blog

By zeosutt, 6 years ago, ,

As you might know, stderr doesn't affect a judgement. Therefore, if you use stderr instead of stdout for debugging, you won't get WA even if you forget to delete (or comment out) the lines for debugging.

Of course, you can never get AC if your solution is wrong in the first place :)

• +13

 » 6 years ago, # |   +22 vector adj[N]; void dfs(int node, int level) { cerr << node << " " << level << "\n"; // do something for (int neighbor : adj[node]) dfs(neighbor); } the runtime of the above code would surely decrease if the cerr statements were removed. and if the recursion runs for nearly 106 nodes, it could easily result in the solution getting TLE instead of AC.
•  » » 6 years ago, # ^ |   +3 We are facing a trade-off between coding time and running time.When our solution seems good, we should remove some debugging statements which consump much time. I think it is good idea.
•  » » 6 years ago, # ^ |   +3 Oh, sorry. I completely forgot an effect on running time. Certainly, the effect of debugging statements in such a case cannot be ignored. Therefore, please think using stderr instead of stdout is only an insurance against WA.
•  » » » 6 years ago, # ^ |   +27 Codeforces defines an ONLINE_JUDGE macro for C/C++ programs. Therefore it is possible to write a template where the debugging output works on a local machine, and turns into nothing on Codeforces. A very simple implementation: #ifndef ONLINE_JUDGE # define LOG(x) (cerr << #x << " = " << (x) << endl) #else # define LOG(x) 0 #endifThen just write LOG(i); in the program.
•  » » » » 6 years ago, # ^ | ← Rev. 2 →   +3 Thanks for a wonderful macro!
 » 6 years ago, # |   0 Deleting cerr's when submitting can be done in a following way: 1. Replace (Ctrl+R in Kate) cerr -> //cerr :PDefining own macros is a good idea, but sometimes we want something mote than just printing the value of a variable (for example additional comments written by us to make them readable). By the way if we have macro in our code like that LOG(x) and use it in a code, we should take care of line with that define in a replace method I explained earlier :P.
•  » » 6 years ago, # ^ |   -14 Well, we may define so that it's as easy to write comments to it as to cerr (Well not very easy:) ) #ifndef ONLINE_JUDGE # define LOG(x) cerr << x << endl; //you may call it as LOG("i want to print " << x << " thats a value of x") #else # define LOG(x) #endif But you should be careful with values like LOG(1<<2)
•  » » 6 years ago, # ^ |   +3 In my actual implementation of LOG() (which uses C++11 variadic templates) this works: the code int a = 42; vector b = { 1, 2, 3 }; LOG(a, b, "comment");will print  main 80: a, b, "comment" = 42, [1, 2, 3], commentIt's not much, but I'll try to polish the code and put it on Github so that other people can see it sometime later.
•  » » » 6 years ago, # ^ |   0 Can you share your source?, the macro LOG(...) is great.
•  » » » » 6 years ago, # ^ |   0
 » 2 months ago, # |   -18 It doesn't give WA but actually it does give TLE check out 76023053 gives TLE and the other 76022926 is Accepted.So it's always better to comment out or delete stderr statements before submitting
•  » » 2 months ago, # ^ |   +26 Yes.That was the idea behind the very first comment written under this post.Six years ago.