This is one of a three-part mini series about how I’m using modern C as of late 2026.
Before C23, I was taken in by How I Program C for years and years, and would even feel guilty for choosing C99 instead of -ansi -pedantic. But holy crap man I’m done being a doomsday prepper! These days I maintain a large-enough project with enough users where I could stand less foot-shooting. (I’ve also got bills to pay.)
So here’s three modern C conventions which started to rise naturally from adding -std=c23 to my zig build:
Our first one is centered around [[nodiscard]]. If I draw an app window or panel I require the caller to interrogate the rect of the thing that was just rendered:
[[nodiscard]] rect_t draw_screen(/* ... */) {
rect_t screen_r = { };
// Draw stuff
// ...
return screen_r;
}
It’s a business logic bug if my caller doesn’t capture the rectangle for later processing. Therefore [[nodiscard]] has been such a godsend for fixing bugs… Except there’s a choice few instances where I will draw something with no genuine use for the resulting rect:
enum screen_opt popup_options = /* ... */ ;
draw_screen(popup_options, /* ... */); // ERROR: damn you [[nodiscard]]
Clang will error out here. I could capture the var and never use it but…
rect_t rect = draw_screen(/* ... */); // ERROR: unused variable (I have `-Werror` enabled)
Pre-C23 I could solve this through an UNUSED() macro:
#ifndef UNUSED
#define UNUSED(x) (void)(x)
#endif
rect_t rect = draw_screen(/* ... */);
UNUSED(rect); // Silences the compiler, but now I'm sad.
But now with C23 I’ve deleted the macro in favor of [[maybe_unused]]:
[[maybe_unused]] rect_t rect = draw_screen(...); // OK
Phew I feel better. I’ve also noticed this is happening all over the place: lots of different routines returning different types that are marked with [[nodiscard]]. So for those few exceptions why not just go for:
[[maybe_unused]] auto _ = foo(); // A new pattern emerges
Bonus: For any macro fans out there a fellow indie dev (Zardium) offered an additional imrpovement. From our chat server:
Zardium: #define _ [[maybe_unused]] auto CONCAT_MACRO(zz,COUNTER)
Abner: ahh, unique varname. nice one
Zardium: you could take the auto out if you don’t want it to look so weird. then it acts exactly like the _ in other languages, where it can be redefined
Abner: Yep totally. Although here I was celebrating my removal of a macro… XD
I’ve been cheated and lied to: designated initializers DO NOT clear my struct to zero and I can’t even trust {0} anymore. (Talk about a betrayal.) The problem is I’ll often have data types like this contrived timestamp:
typedef struct {
Type type;
char buf[MAX];
union {
time_t time;
float dt;
date_t date;
};
} stamp_t;
And if I partially initialize one:
stamp_t stamp = { .type = STAMP_TYPE_BLA_BLA };
While it does mean we successfully zeroed out buf (thanks to empty initialization) those union members are just a different beast. My dear reader: I’ve made the costly mistake of assuming date would clear to zero!
As I Spongebob-panicked in public Lobsters member accelbread offered a sage revelation:
accelbread: It used to be that GCC would fully zero the union anyways, and clang would only zero the time_t, though around a year ago they swapped behaviors iirc. Either way, standard only requires the time_t be zeroed and not whole union. GCC has a flag to always zero whole union. Also C23 initialization always inits whole union
Wait WHAT? clang and GCC SWAPPED what now? I won’t investigate further. Everything about this is dangerous af unless we hug C23 tightly and never let go:
stamp_t stamp = { };
stamp.type = STAMP_TYPE_BLA_BLA;
Accelbread went on to say two more things:
Yessir.
If I want to customize some dialog box I’ll use bit flags:
enum {
OPT_AUTOSCROLL = (1 << 0),
OPT_NOCURSOR = (1 << 1),
OPT_CENTERED = (1 << 2),
OPT_NOCLOSE = (1 << 3),
// ...
};
[[nodiscard]] bool draw_warning(const char* msg, int opt);
Even if we disagree with this approach lots of relevant libraries or projects do it:
_ = draw_warning("you done messed up A-A-RON", OPT_CENTERED | OPT_NOCLOSE);
Of course, erroneous bit shifting will land anyone into trouble and yield comical numbers. Thankfully C enums are a plain int underneath so the compiler will warn us if we defined a bad constant inside the enum that won’t fit.
:)
I’m kidding. Sigh. Well, I’m growing fearful of sage revelations but this one comes from Modern C by Jens Gustedt:
Jens: If enumeration constants do not fit into signed int, if possible, the enumeration type is adjusted such that it can store all enumeration constants.
Noooooo!
Jens: The property that an an enumeration type is adjusted such that it fits all its constants could have surprising effects
sobs
Jens: So, it is preferable to specify the underlying integer type explicitly
THERE IS HOPE?
enum options : int {
OPT_AUTOSCROLL = (1 << 0),
OPT_NOCURSOR = (1 << 1),
OPT_CENTERED = (1 << 2),
OPT_NOCLOSE = (1 << 3),
// ...
};
It compiles! We shoot. We score. We stick with C23.
In part two of our mini series I’ll discuss three more conventions that I’ve fleshed out thanks to modern C: starting with safer macro usage (forgive me Zig folks.)
P.S. If you want to shape this discussion maybe join the Handmade Cities server!
-Abner