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C++ std::min function does not seem to return correctly when using it on two std:array objects
By idk321, history, 3 years ago, In English

Take a look at the end of these two programs:

https://atcoder.jp/contests/abc188/submissions/19361247

https://atcoder.jp/contests/abc188/submissions/19361394

One is correct and the other is not, even though in theory the one with std::min should be equivalent, since the first values of the arrays are all pairwise distinct.

EDIT: std::array variable holding fundamental types of local scope is not zero initialized (unlike other containers to my knowledge).

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3 years ago, # |
← Rev. 2   Vote: I like it +5 Vote: I do not like it

I've initialized array in the second submission and got AC. But I have no idea why your first solution works, it passed in 3 out of 3 tries.

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    3 years ago, # ^ |
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    Seriously? Huh, why do you think it is like that, considering the fact, that the array should at least in theory be default initialized with zeores? Oh wait, it isn't?

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      3 years ago, # ^ |
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      std::array declared locally goes on the stack and isn't zero-initialized (as with any locally declared primitive types).

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      3 years ago, # ^ |
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      std::array, unlike std::vector, does not zero-initialize its elements by default. Use std::array<T, N> var{}; to zero-initialize.

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      3 years ago, # ^ |
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      Array uses default initialization.

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    3 years ago, # ^ |
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    Oh it says so in the documentation. Thank you, I falsely assumed that like other std containers its elements are also zero initialized.

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      3 years ago, # ^ |
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      std::vector is zero-initialized because its data is allocated on the heap (even if the vector is declared locally).

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      3 years ago, # ^ |
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      You should read warnings next time. Atcoder shows compilation log right below the code.

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3 years ago, # |
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Auto comment: topic has been updated by idk321 (previous revision, new revision, compare).

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