检查两个2D数组是否相等

Question

How can I tell if two 2D arrays exactly match every element? They have equal dimensions.

std::equal does not seem to work.

I tried to write a simple function

bool arrays_equal(int a[][], int b[][])
{
...
}

but then I need the last dimension of both arrays to pass a two dimensional array. Would that be done using (sizeof(a[0])/sizeof(*(a[0]))) ?

Answer 1

Maybe like this?

bool arrays_equal(std::array<std::array<int, M>, N> const & lhs,
                  std::array<std::array<int, M>, N> const & rhs)
{
    return lhs == rhs;
}

The values M and N should be your array dimensions, or you could make them function template parameters. Don't forget to #include <array> .

Answer 2

Assuming you know the exact size of each array and they are known at compile time, then the compare is just a memcmp() with the correct size.

// you somehow know the size of the array
int a[WIDTH][HEIGHT];
int b[WIDTH][HEIGHT];

bool const equal(memcmp(a, b, sizeof(int) * WIDTH * HEIGHT) == 0);

// and if defined in the same scope, you can even use:
bool const equal(memcmp(a, b, sizeof(a)) == 0);

Note that my code assumes that both arrays (a and b) have the same size. You could test that first to make sure, with a throw or maybe an assert such as std::assert(sizeof(a) == sizeof(b)).

In case you don't know the size at compile-time sizeof won't work since it's a compile-time operator, which means you'll have to pass the dimensions or consider using stl .