C language: passing small structures by value ¶

Posted on Sat Feb 18, 2017

In my CCEvents project (still in early development) I started using “small” data structures as values. I’m talking about structures that are 2, 3 or 4 words in size, like posix’s struct timeval and these ones:

struct ccevents_timeval_t {
  struct timeval;
};

struct ccevents_timeout_t {
  long int      seconds;
  long int      milliseconds;
  long int      microseconds;
};

So I write code like this:

#include <ccevents.h>

cce_location_t          L[1];

if (cce_location(L)) {
  cce_run_error_handlers(L);
  cce_condition_free(cce_condition(L));
} else {
  ccevents_timeout_t    to = ccevents_timeout_init(L, 1, 2, 3);
  ccevents_timeval_t    tv = ccevents_timeout_start(L, to);

  if (ccevents_timeval_is_expired_timeout(tv)) {
    /* do something */
  }
  cce_run_cleanup_handlers(L);
}

and just accept the performance penalty of copying data structures on the stack both as parameters and return values.

I find the code significantly clearer to write without pointers; there are no NULL pointers problems; memory allocation management is simpler; there is less sharing of contexts; and I can also specify significant gcc attributes for functions that I could not add when using pointers (some functions become ‘leaf’, ‘const’ or ‘pure’; see gcc’s documentation for details).