Don't know why you are voted down, string processing is indeed unpleasantly difficult in C. Partly because a built-in string type would conflict with C's simplistic compile/link schema.
https://news.ycombinator.com/item?id=7191509
I've used Ustr before, all of them have pros and cons depending on what you are needing.
The volume of string libraries only suggests how crucial core library design, often an afterthought, is to programming language design. The language itself encourages idioms, and it's for the core library to harness these idioms into a robust, cohesive, comprehensive toolbox for common tasks.
My article about it:
foo(size_t n, char arr[restrict static n])
The static qualifier here means "no really, I actually want the compiler to complain if the passed array isn't the size indicated". (because C doesn't have enough different meanings for the word "static" :( ). I haven't seen this in the wild yet or checked if gcc and clang actually implement it usefully, but it seems like it could be quite useful.