C语言前提条件和后置条件
示例
声明的一种用例是前置条件和后置条件。这对于按合同维护不变性和设计非常有用。例如，长度始终为零或正，因此此函数必须返回零或正值。
#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;
}