stderr doesn't affect a judgement

Блог пользователя zeosutt

Автор zeosutt, 12 лет назад, По-английски

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 :)

stderr, debug

zeosutt
12 лет назад
15

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JuanMata

12 лет назад, скрыть # |

+22

vector<int> 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.

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kien_coi_1997

12 лет назад, скрыть # ^ |

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.

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zeosutt

12 лет назад, скрыть # ^ |

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.

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andreyv

12 лет назад, скрыть # ^ |

+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
#endif

Then just write LOG(i); in the program.

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zeosutt

12 лет назад, скрыть # ^ |

← Rev. 2 →

Thanks for a wonderful macro!

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Swistakk

12 лет назад, скрыть # |

Deleting cerr's when submitting can be done in a following way: 1. Replace (Ctrl+R in Kate)

cerr -> //cerr

Defining 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.

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riadwaw

12 лет назад, скрыть # ^ |

-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)

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andreyv

12 лет назад, скрыть # ^ |

In my actual implementation of LOG() (which uses C++11 variadic templates) this works: the code

int a = 42;
vector<int> b = { 1, 2, 3 };

LOG(a, b, "comment");

will print

 main 80: a, b, "comment" = 42, [1, 2, 3], comment

It'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.

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Ziklon

12 лет назад, скрыть # ^ |

Can you share your source?, the macro LOG(...) is great.

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MrDindows

12 лет назад, скрыть # ^ |

http://ideone.com/y39aaF

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manojeet24

6 лет назад, скрыть # |

-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

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-is-this-fft-

6 лет назад, скрыть # ^ |

+26

Yes.

That was the idea behind the very first comment written under this post.

Six years ago.

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aKILLL

4 года назад, скрыть # |

I'm getting WA while using stderr. wrong solution using cerr (debug(u)) 178151957. Correct solution by commenting that line 178151812. Am I missing something?

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