I came across this question regarding sorting the first 2 lines of an array of integers, the obvious way that came to mind was to use std::sort so I proposed a solution like:
int mat[][3] = { {4, 5, 3},
{6, 8, 7},
{9, 5, 4},
{2, 1, 3} };
std::sort(std::begin(mat[0]), std::end(mat[1])); //sprting the first two rows
As you can see here it works without errors or warnings.
Meanwhile @Jarod42 pointed out that this is pedantically undefined behaviour in C++ because these are pointers of two different arrays.
I inclined towards this given that in C this would be a good way to do it, (without the std::sort, std::begin and std::end of course), using a similar method of accessing the array in line, given the way 2D arrays are stored in C.
We agreed that it would be undefined behaviour, but as @SergeBallesta remebered, pretty much all compilers accept this method, so should it be used?
And what about if one uses a int(*mat)[3] pointer to array, would it still be pedantic UB to use std::sort this way?
//...
srand(time(0));
int(*mat)[3] = (int(*)[3])malloc(sizeof(int) * 4 * 3);
//or int(*mat)[3] = new int[4][3];
for(int i = 0; i < 4 ; i++)
for(int j = 0; j < 3; j++)
mat[i][j] = rand() % 9 + 1;
std::sort(std::begin(mat[0]), std::end(mat[1])); //sorting the first two rows
//...
