memset0c's blog

How to output long double values using printf on codeforces?
By memset0c, history, 4 years ago, In English

Excuse me, can anyone tell me how to use printf to output long double values?

I tried to use %Lf, but it just output zero when I chose GNU C++11.

However, I got AC when choosing GNU C++17 (64).

Can anyone tell me what should I do? Thank you~

GNU C++11 submission (WA on 1): https://mirror.codeforces.com/contest/1209/submission/92331960

GNU C++17 (64) submission (AC): https://mirror.codeforces.com/contest/1209/submission/92331832

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4 years ago, # |
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Just use GNU C++17 (64)

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4 years ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

If you're down with cout then,

std::cout<<std::setprecision(10)<<ans<<std::endl;

This worked -> Here

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    4 years ago, # ^ |
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    It still doesn't work with GNU C++11.

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      4 years ago, # ^ |
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      I have used simple cout in your code with both C++14 and C++11 with outputs 361.569 and 1000 respectively.

      Now I don't think this is possible unless you've used something else that is broken in C++11. I might be wrong.

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        4 years ago, # ^ |
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        Only using std::cin & std::cout instead of scanf & printf can it work with GNU C++11.

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4 years ago, # |
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A tangential answer: note that, most of the time, casting to a double would be fine in output, as a relative error of $$$10^{-9}$$$ is allowed.

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    4 years ago, # ^ |
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    well, it's quite complicated.

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      4 years ago, # ^ |
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      Huh? How much more complicated is printf ("%.6lf", (double) (x));?

      Instead of just printf ("%.6Lf", x);.

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        4 years ago, # ^ |
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        I also need to use 

        double temp;
scanf("%lf", &temp);
target = temp;

        instead of

        scanf("%Lf", &temp);
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          4 years ago, # ^ |
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          Yeah, that, too. But reading and writing values is an easy part of the problem. Usually.

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4 years ago, # |
  Vote: I like it +36 Vote: I do not like it

Short answer is, you don't. The implementation used by codeforces's version of C++11 does not implement printf for long doubles.

You can switch to the mingw implementation by either submitting in C++11 with #define __USE_MINGW_ANSI_STDIO 1 before your code, or by submitting in C++17 (64). Be aware though that mingw printf is slow so you are exposing yourself to potential TLEs by doing this.

To be safe, I would either switch to using cout and a more recent version of C++, or use C++11 printf after casting to double.

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4 years ago, # |
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This is very off-topic but turns out you can put image as a background for your text on cf
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