Reverse order of rows in 2d array - c

Question

I'm trying to figure out how to "flip" an 2d array like this:
{{1, 2, 3},
{4, 5, 6},
{7, 8, 9}}
{{7, 8, 9},
{4, 5, 6},
{1, 2, 3}}
Searching how to reverse/flip rows of 2D array just returns how to reverse the content of the rows, or some other variation that doesn't work like I need

Answer 1

Swapping rows work exactly the same way as swapping integers, only instead of assigning you need to copy the memory.
void reverseRows(size_t rows, size_t cols, int (*array)[cols])
{
int temp[cols];
size_t last = rows - 1, first = 0;
while(last > first)
{
memcpy(temp, array[first], sizeof(*array));
memcpy(array[first++], array[last], sizeof(*array));
memcpy(array[last--], temp, sizeof(*array));
}
}
#define N 3
int main(void)
{
int a[N][N] =
{
{ 1, 2, 3 },
{ 4, 5, 6 },
{ 7, 8, 9 }
};
for ( size_t i = 0; i < N; i++ )
{
for ( size_t j = 0; j < N; j++ )
{
printf( "%d ", a[i][j] );
}
putchar( '\n' );
}
putchar( '\n' );
reverseRows(N,N,a);
for ( size_t i = 0; i < N; i++ )
{
for ( size_t j = 0; j < N; j++ )
{
printf( "%d ", a[i][j] );
}
putchar( '\n' );
}
}
https://godbolt.org/z/qxW3rG3sx

Answer 2

Here you are.
#include <stdio.h>
void swap_arrays( int *a1, int *a2, size_t n )
{
for ( size_t i = 0; i < n; i++ )
{
int tmp = a1[i];
a1[i] = a2[i];
a2[i] = tmp;
}
}
int main(void)
{
enum { N = 3 };
int a[N][N] =
{
{ 1, 2, 3 },
{ 4, 5, 6 },
{ 7, 8, 9 }
};
for ( size_t i = 0; i < N; i++ )
{
for ( size_t j = 0; j < N; j++ )
{
printf( "%d ", a[i][j] );
}
putchar( '\n' );
}
putchar( '\n' );
for ( size_t i = 0; i < N / 2; i++ )
{
swap_arrays( a[i], a[N - i - 1], N );
}
for ( size_t i = 0; i < N; i++ )
{
for ( size_t j = 0; j < N; j++ )
{
printf( "%d ", a[i][j] );
}
putchar( '\n' );
}
putchar( '\n' );
return 0;
}
The program output is
1 2 3
4 5 6
7 8 9
7 8 9
4 5 6
1 2 3