Effective to use const struct in C instead of defines for grouping configuration parameters?

Question

I am thinking of using a global constant struct to manage configuration of some sub-systems. This means that I would like to use something like:

const struct SystemConfig {
  .channels = 5,
  .mode = NORMAL_MODE,
} SYSTEM_CONFIG;

And later use it in my code like usual:

...
numberOfChannels = SYSTEM_CONFIG.channels;
mode = SYSTEM_CONFIG.mode;
...

I would like to use this approach to skip #define's.

My question is if the compiler will realize this and replace the values with their respective values when it is compiled, considering everything is constant?

EDIT: Sorry for tagging both C and C++, it's fixed now and my question relates only to C. The compiler I use is GCC with a ARM Cortex-M4 target.

The only way to find out is to look at the generated assembler code. — Some programmer dude, Feb 15 '13 at 14:07
`...if the compiler will...` which compiler? And since it's tagged with both C and C++, which language? — Mike, Feb 15 '13 at 14:08
Even if the compiler doesn't special case it, how much difference is it going to make to runtime of your code in practice? The mechanism is quite neat and tidy; use it if you think the notational clarity is worthwhile (it might well be worth it). — Jonathan Leffler, Feb 15 '13 at 14:54
@Niklas Norin Are you familiar with design patterns? Have you considered the Singletone pattern, it quit good fits to your needs, as you described them in your question — spin_eight, May 08 '13 at 17:43

score 0 · Answer 1 · edited May 08 '13 at 17:20

I would use static const so your struct is not visible at link level. For example:

static const unsigned int channels = 5;
unsigned numberOfChannels = channels;

would definitely be optimised by a compiler. So I can't see why any modern compiler would be unable to optimise your example either.

If it was me I would find the compiler option to output the code it was laying down. It's an interesting exercise.

Effective to use const struct in C instead of defines for grouping configuration parameters?

1 Answers1