I figured out why this was happening for me. I was trying to add a null pointer to the end of the buffer using the strlen() call, but, obviously, as there wasn't a null pointer in the buffer already, strlen just went until the most recent pointer and added one in the same place.

C lang : My solution is passing the test but failing the attempt. When it fails the attempt it is because on longer strings in the ACTUAL return it is giving a load of garbage characters at the start and then the rest of the response matches the expected.

When I add code in to shift the pointer to start after these garbage characters I then get pointer error.