#Pointer comparisons

24 messages · Page 1 of 1 (latest)

opal trench
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bool vectorContains(std::vector<DataType>& vec, DataType& data) { 
  return (&data >= &*vec.begin()) && (&data < &*vec.end());
}

if i have an element by reference, theoretically, one could check for its existence inside the vector like this, right?

wheat mountainBOT
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opal trench
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@topaz hatch we can discuss here so that the text channel does not get cluttered

topaz hatch
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But yeah, basically, the standard only defines pointer comparison for different pointers when:

  • Two pointers in the same array
  • Two pointers to different data members (non static) of the same object, subobjects of that object (recursively) when the subobjectis not zero sized or a union
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Any other comparisons are not defined. So, your vector contains is only well defined if it indeed contains the object

opal trench
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right

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so my original problem was that, i have a pointer to an object i am sure is contained in one of two vectors, and i want to determine which vector the object is in because i want to remove the object from the corresponding vector. is there a way to do this without resorting to linear search?

topaz hatch
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Is the data sorted?

opal trench
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no

topaz hatch
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Then linear it is

opal trench
topaz hatch
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You could also use a bloom filter as an early out, but that's only a test for does not contain, it doesn't prove that it contains

opal trench
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i see

topaz hatch
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If you need a cheap lookup, you can use a hash set too, instead of a vector

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But if your data set is small, linear search is cheap

opal trench
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i see

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i am going to be iterating through this container a lot so i want to use a vector

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well i found another fix for my problem in context what i am doing

opal trench
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pointer1 + pointer2

topaz hatch
opal trench
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indeed

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!solved