Should be titled "without using malloc" or something. It's pretty much impossible to do anything with user input strings unless you have some sort of memory management. Maybe you have one giant buffer that you use for strings in a particular session, but that still involves memory management because even if you allocate the buffer at startup, using one buffer for multiple strings is just a type specific arena allocator.

As someone who works on low level database code, this approach is going to be EXTREMELY wasteful. Instead, it's much better to instead have a more sophisticated understanding of memory use by subsystems and have some concept of required memory and caches. Each system allocates the minimum memory it needs at startup and then treats the rest of memory as caches which can be emptied as necessary to preserve fairness among all the various subsystems.