Assertions on doubles with variable precision

assert_double.c

/*
Assertions on doubles are tricky in C, because of the way precision is handled.  The default precision
used in things like displaying and comparing is 6 decimal places, even though the internal precision value
is much higher.  This makes things like assertions difficult, if you want to assert on any value other
than the default 6 decimal places.  Here's a way to do it by converting both values to strings before
the assertion.
*/

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>

void assert_doubles(double compare1, double compare2, int places);

int main()
{
	double hours = 18.0;
	double minutes = 31.0;
	double seconds = 27.0;

	double a = fabs(seconds) / 60.0;
	double b = (fabs(minutes) + a) / 60.0;
	double c = fabs(hours) + b;
	double d = (hours < 0.0 || minutes < 0.0 || seconds < 0) ? -(c) : c;

	printf("Result is %0.8f\n", d);
	assert_doubles(d, 18.52416667, 8);

	return (0);
}

void assert_doubles(double compare1, double compare2, int places)
{
	char compare_string1[50];
	char compare_string2[50];

	sprintf(compare_string1, "%0.*f", places, compare1);
	sprintf(compare_string2, "%0.*f", places, compare2);

	assert(strcmp(compare_string1, compare_string2) == 0);
}