Making a StringBuffer in C, and questioning my sanity

It can be refactored into creating a buffer primitive of void* buf, size_t capacity, size_t refcount. Then, the string can implement using CoW logic on a buffer and size_t length. Read-only references to substrings become cheap and copying is done whenever there's a modification or realloc can't grow the underlying buffer.

    new_capacity *= 2;

https://stackoverflow.com/questions/1100311/what-is-the-idea...

Hm, this implementation seems allergic to passing types by value, which eliminates half of the allocations. It also makes the mistake of being mutable-first, and provides some fundamentally-inefficient operations.

The main mistake that this makes in common with most string implementations make is to only provide a single type, rather than a series of mostly-compatible types that can be used generically in common contexts, but which differ in ways that sometimes matter. Ownership, lifetime, representation, etc.

It's odd how it has error reporting in some areas (alloc, split can return NULL if allocation fails), but not others (append, prepend have a void return type but might require allocation internally).

You might be interested in https://github.com/antirez/sds

I would rather focus on solving the main problem than reinvent the wheel. Just use C++ if perf is critical which gives you all these things for free. In this day and age the reasons for using C as your main language should be almost zero.