I've been using mostly C at my current job for about half a year now, and I find myself reusing some little function that I've written for another code base in current projects. I'm relatively new to this, so I'm wondering if it makes sense to have a repertoire of general purpose utility functions and whatnot for future use.

I mean, the language's pretty established and whatever I think of must have been written by somebody else already, so is there even a need for what I'm talking about? Are there well-known open source libraries that resemble what I am talking about? Should I just include them instead of writing my own?

Sorry if this is a bit vague. General purpose as in string manipulation, debug output, buffer operations, implementations of data types not in C, etc., just to name a few examples.