C Language Assertion Precondition and Postcondition
Example
One use case for assertion is precondition and postcondition. This can be very useful to maintain invariant and design by contract. For a example a length is always zero or positive so this function must return a zero or positive value.
#include <stdio.h>
/* Uncomment to disable `assert()` */
/* #define NDEBUG */
#include <assert.h>
int length2 (int *a, int count)
{
int i, result = 0;
/* Precondition: */
/* NULL is an invalid vector */
assert (a != NULL);
/* Number of dimensions can not be negative.*/
assert (count >= 0);
/* Calculation */
for (i = 0; i < count; ++i)
{
result = result + (a[i] * a[i]);
}
/* Postcondition: */
/* Resulting length can not be negative. */
assert (result >= 0);
return result;
}
#define COUNT 3
int main (void)
{
int a[COUNT] = {1, 2, 3};
int *b = NULL;
int r;
r = length2 (a, COUNT);
printf ("r = %i\n", r);
r = length2 (b, COUNT);
printf ("r = %i\n", r);
return 0;
}
