Handling errors

[errant leaf]

Hi! I'm trying out Advent of Code in Zig, starting on day one 🙂

When using parseInt in a string I should sometimes get an error (which is a good thing!) however I want to use the error to continue the loop i'm currently running. How should I go about it?

Using orelse undefined and then checking if var is undefined could work? 🤔

So If i get an error, I continue. Otherwise I use the parsed integer in the rest of the code.

[scenic creek]

undefined is not something you can compare against, it's a meaningless value

std.fmt.parseInt(...) catch continue;

[errant leaf]

cant i do smthg like if(temp == undefined)

[scenic creek]

you can but it absolutely will not do what you want and it's never something that should be done

I think it will be disallowed soon as well

[errant leaf]

Ok thanks 🙂 I must be missing something else too though

[scenic creek]

catch and try are exclusive so just remove the try

[errant leaf]

ahh ok, makes sense

Yep, that worked, just need to fix some types mismatches and should be working 🙂

Thanks!

[scenic creek]

np

[errant leaf]

can I put more than one line of code in the catch statement?

[scenic creek]

yeah just add curly brackets after catch

[simple widget]

zig undefined is not like undefined in js. zig's undefined means 'whatever happens to already be at this address' rather than some concrete value.

so comparing undefined to undefined is like comparing 'whatever happens to already be here' with 'whatever already happens to be there'

which doesnt not make much sense

just felt that this part deserved a bit more detail :D

[errant leaf]

Yh, meanwhile I read a bit more and understood that. Thanks 🙂 got my AoC day 1 done

[errant leaf]

It's pretty much malloc from what i understood.

[scenic creek]

in the sense that the memory you get from malloc is undefined but theyre 2 very different things

zigs var foo: i32 = undefined; is effectively equivalent to Cs int foo;, nothing to do with memory allocation

[errant leaf]

Doesnt the declaration of int foo reserve de memory needed for the int? Thus being an allocation

[scenic creek]

technically yes but its rare that someone refers to that as "allocation"

allocation usually is used to refer to dynamic allocation e.g. malloc

[vagrant dome]

the closer approximation wrt to how the memory is allocated would be alloca

the heap and the stack are (generally) two very different regions of the address space

allocating on the stack is about as expensive as incrementing a pointer (as in, the stack pointer)