Question

Is the defacto method for comparing arrays (in C) to use memcmp from string.h?

I want to compare arrays of ints and doubles in my unit tests

I am unsure whether to use something like:

double a[] = {1.0, 2.0, 3.0};
double b[] = {1.0, 2.0, 3.0};
size_t n = 3;
if (! memcmp(a, b, n * sizeof(double)))
    /* arrays equal */

or to write a bespoke is_array_equal(a, b, n) type function?

Answer 1

memcmp would do an exact comparison, which is seldom a good idea for floats, and would not follow the rule that NaN != NaN. For sorting, that’s fine, but for other purposes, you might to do an approximate comparison such as:

bool dbl_array_eq(double const *x, double const *y, size_t n, double eps)
{
    for (size_t i=0; i<n; i++)
        if (fabs(x[i] - y[i]) > eps)
            return false;
    return true;
}