Question: The C standard library is notoriously poor when it comes to I/O safety. Many functions have buffer overflows (`gets`, `scanf`), or can clobber memory if not given proper arguments (`scanf`), and so on. Every once in a while, I come across an enterprising hacker who has written his own library that lacks these flaws.

What are the best of these libraries you have seen? Have you used them in production code, and if so, which held up as more than hobby projects?

Answer: 
This isn't really answering your question about the safest **libraries** to use, but most functions that are vulnerable to buffer overflows that you mentioned have safer versions which take the buffer length as an argument to prevent the security holes that are opened up when the standard methods are used.

Unless you have relaxed the level of warnings, you will usually get compiler warnings when you use the deprecated methods, suggesting you use the safer methods instead.
You're always at liberty to implement any library you like and to use it - the hard part is making sure it is available on the platforms you need your software to work on. You can also use wrappers around the standard functions where appropriate.

Whether it is really a good idea is somewhat debatable, but there is TR24731 published by the C standard committee - for a safer set of C functions. There's definitely some good stuff in there. See this question: [Do you use the TR 24731 Safe Functions in your C code?](https://stackoverflow.com/questions/372980/do-you-use-the-tr-24731-safe-functions-in-your-c-code), which includes links to the technical report.