exceptions4c is a tiny, portable framework that brings the power of exceptions to your C applications. It provides a simple set of keywords (macros, actually) which map the semantics of exception handling you're probably already used to: try, catch, finally, throw. You can write try/catch/finally blocks just as if you were coding in Java. This way you will never have to deal again with boring error codes, or check return values every time you call a function.
LibLogicalAccess is an RFID library developed in C++ for Linux/Windows, also available on C# for use on Microsoft operating systems (using a COM wrapper). It provides low-level commands access and high-level generic abstraction for several chips and readers (PC/SC readers like OMNIKEY, STid readers, etc.) on 125Khz (EM4102, HID Prox, etc.), 13.56Mhz ISO14443/ISO15693 (Mifare Classic, Mifare DESFire, HID iClass, etc.), and 433Mhz frequencies.
MLPACK is a C++ machine learning library with an emphasis on scalability, speed, and ease-of-use. Its aim is to make machine learning possible for novice users by means of a simple, consistent API, while simultaneously exploiting C++ language features to provide maximum performance and maximum flexibility for expert users. It contains algorithms such as k-means, Gaussian mixture models, hidden Markov models, density estimation trees, kernel PCA, locality-sensitive hashing, sparse coding, linear regression and least-angle regression.