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Explain yourselves, comp sci. (mander.xyz)

submitted 3 months ago by [email protected] to c/[email protected]

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[–] [email protected] 72 points 3 months ago (13 children)

[–] [email protected] 81 points 3 months ago* (last edited 3 months ago) (7 children)

It's a dynamically-sized list of objects of the same type stored contiguously in memory.

dynamically-sized: The size of it can change as needed.

list: It stores multiple things together.

object: A bit of programmer defined data.

of the same type: all the objects in the list are defined the same way

stored contigiously in memory: if you think of memory as a bookshelf then all the objects on the list would be stored right next to each other on the bookshelf rather than spread across the bookshelf.

[–] [email protected] 15 points 3 months ago (6 children)

Dynamically sized but stored contiguously makes the systems performance engineer in me weep. If the lists get big, the kernel is going to do so much churn.

[–] [email protected] 7 points 3 months ago* (last edited 3 months ago)

Which is why you should:

Preallocate the vector if you can guesstimate the size
Use a vector library that won't reallocate the entire vector on every single addition (like Rust, whose Vec doubles in size every time it runs out of space)

Memory is fairly cheap. Allocation time not so much.

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