Is there anything else needed for approval?

Yes. This is the fork to approve. I have just finished adding the suggestion you made with the not null assert, so it should be ready.

That does seem cleaner. I was unaware of this assert before, so thanks for pointing it out.

in some places you have a pattern of:

if( someptr == NULL ){
  cr_assert_fail( "canot be null" );
} else {
  ... more testing code...
}

It could be probably replaced (or at least I think so) with

cr_assert_not_null(someptr, "cannot be null");
... more testing code...

Would it be this fork to be approved?

So if no one else has any comments/additions, will this be approved?

@nomennescio I swapped out slightly ugly syntax in favor of a typedef typedef int (*SudokuBoard_t)[ 9 ].

In addition, the relabeling now permutates 1-9, instead of only swapping 3 pairs of integers.

@Bats6789 as for formatting, you can pick any style you like, look around at some code of others, what you think is most readable.

As for relabeling, I think it should apply to all numbers i.e. do a permutation on 1-9.

@Hobovsky Ah, I see, I missed the "easy that can be solved by brute force" tag.

@hobovsky the translation now applies some random relabelling like so

for( int j = 0; j < 3; ++j ){
  a = rand();
  b = rand();
  if( a != b ){
    relabel( puzzle, a, b ); // change all a->b, and b->a
    relabel( answer, a, b );
  }
}

The relabeling occurs before every transformation that was there before. So effectively the steps are:

1. grab a pre-written puzzle and solution
2. relabel puzzle and solution the same way
3. transform puzzle and solution the same way

Is this a sufficient relabeling/randomization strategy?

@nomennescio What would be the standard format? I'm willing to modify the code to comply with the standard.

Generating a solvable sudoku of a specific difficulty is hard. It was tried by other translations, and general consensus is that's it's too difficult to do reliably. As an alternative, other translations (and I advised to do the same thing here) is to use some predetermined boards and transform them randomly by relaellings, rotations, and swapping row/column triples. As far as I see, the translation does not do relabellings, which, I think, have the biggest "obfuscation" potential.

If you can come up with a reliable way of generating easy, solvable boards, feel free to share.

That looks much better, although I find the formatting a bit non-standard, but I'm willing to ignore that.
However, the random tests are basically scrambling a pre-calculated solution, which is not random enough.
I expect that you fill a random puzzle, and call your own solver to find the reference solution, and test the user's solution against that.

@nomennescio I decided to convert to a contiguous 2D array. It was a fun little learning experience for me. Everything should be converted over now.

I do recognize that 2D arrays in C are quite difficult to get right, that's why I suggested the struct (which can be assigned and returned as regular values)