Brain teaser: what does this switch statement print?

https://gist.github.com/theonewolf/5486167

by theonewolf • 13 years ago

25 18 13 years ago

gist.github.com

A nefarious programming bug awaiting all C programmers...especially when coding on low sleep!

cypherpunks01• 13 years ago

Is this supposed to reveal something insightful about switch statements in C?

theonewolf7• 13 years ago

That you can compile with with labels instead of _any_ actual case statements :-) although your source, at a cursory glance, looks like it has valid cases defined.

dmbass• 13 years ago

Maybe if you've never written C before...

dllthomas• 13 years ago

This is why you compile with -Wall and -Werror...

bichiliad• 13 years ago

Don't you need to say "case" before every case statement?

theonewolf7• 13 years ago

Precisely the issue, very easy to miss, still compiles, looks normal.

_ZeD_2• 13 years ago

    $ echo $CFLAGS
    -Werror -Wall -Wextra -Wold-style-definition -Wmissing-declarations -Wredundant-decls -Wmissing-noreturn -Wshadow -Wpointer-arith -Wcast-align -Wwrite-strings -Winline -Wformat-nonliteral -Wformat-security -Wswitch-enum -Wswitch-default -Winit-self -Wmissing-include-dirs -Wundef -Waggregate-return -Wmissing-format-attribute -Wnested-externs -std=c11 -pedantic

Denzel• 13 years ago

Not really a brain teaser: the only case being the default, and the rest simply being labels, makes for a very straightforward program.

theonewolf7• 13 years ago

Right, the point being that you can compile an "almost correct"-looking switch statement with labels instead of actual case statements.

matthavener• 13 years ago

Every time I forget to type "case " I'm instantly corrected when my editor (rightly) removes all indentation and puts the label on the leftmost column.

theonewolf7• 13 years ago

vim? My editor does this too thank God :-)

niggler• 13 years ago

No discussion of C switch statements is complete without a reference to Duff's device: https://en.wikipedia.org/wiki/Duffs_device

theonewolf7• 13 years ago

You had me at: "interlacing the structures of a switch and a loop"

bitbckt• 13 years ago

-Wswitch-enum

_ZeD_2• 13 years ago

-Werror=switch-enum -Werror=unused-label

(but you get the point :D)

theonewolf7• 13 years ago

that's why it's a "Brain teaser" and not a "compiler teaser."

If you were inspecting code without a compiler it's easier to miss.

The standard '-Wall -Werror' catches it (arguably, it'd be nice if everyone _at least_ did -Wall by default).

nikbackm• 13 years ago

How obvious!

And yet I missed it :(

Brain teaser: what does this switch statement print?

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