[GitHub] [arrow] lidavidm commented on issue #10788: How to read a boolean column in C++

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lidavidm commented on issue #10788:
URL: https://github.com/apache/arrow/issues/10788#issuecomment-885606033


   In all cases, you may prefer to downcast to the concrete Array subclass and use accessor methods. In this case that would be Int64Array, StringArray, and [BooleanArray](https://github.com/apache/arrow/blob/3f592a0a24432d3eee9f66081714e7cf4f9928f5/cpp/src/arrow/array/array_primitive.h#L76). BooleanArray has a Value() method that gets the value at a particular index, and of course all arrays have IsValid/IsNull methods.
   
   Indeed, the encoding of a Boolean array is one boolean per bit. You can see this in the definition of `BooleanArray::Value` above. You'll have to take into account the offset as well in case the array is a slice. (Hence the zeroth value in an array lies at the `offset + 0`th bit.)


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