Unexpected results from ut_compare

[mcflugen]

👋 Hi All!

I'm getting some unexpected results with the ut_compare function. The issue may simply be that I misunderstand what it means for one unit to be greater than or less than another. In any case, here is some code that demonstrates what I'm seeing,

#include <stdio.h>
#include <udunits2.h>

int main() {
    ut_set_error_message_handler((ut_error_message_handler) ut_ignore);
    ut_system *sys = ut_read_xml(NULL);
    ut_encoding enc = UT_UTF8;
    ut_set_error_message_handler((ut_error_message_handler) vprintf);

    char *first_unit, *second_unit;
    int i, cmp;
    char *first_units[5] = {"m", "m", "km", "kg", "g"};
    char *second_units[5] = {"km", "cm", "cm", "cg", "kg"};

    for (i=0; i<5; i++) {
	first_unit = first_units[i];
	second_unit = second_units[i];

	ut_unit *u_first = ut_parse(sys, first_unit, enc);
	ut_unit *u_second = ut_parse(sys, second_unit, enc);

	cmp = ut_compare(u_first, u_second);

	if (cmp < 0) {
	    printf("%d) %s is less than %s\n", i + 1, first_unit, second_unit);
	} else if (cmp > 0) {
	    printf("%d) %s is greater than %s\n", i + 1, first_unit, second_unit);
	} else {
	    printf("%d) %s is equal to %s\n", i + 1, first_unit, second_unit);
	}
	ut_free(u_first);
        ut_free(u_second);
    }

    ut_free_system(sys);
    return 0;
}

Running this gives the following output,

1) m is less than km
2) m is less than cm
3) km is greater than cm
4) kg is less than cg
5) g is greater than kg

The output I would expect would be,

1) m is less than km
2) m is greater than cm
3) km is greater than cm
4) kg is greater than cg
5) g is less than kg

Am I doing something wrong here or not understanding what it means to compare units?

System info:

• udunits2 version: 2.2.28
• macos, gcc