GNU gperf is a perfect hash function generator. For a given list of strings, it produces a hash function and hash table, in form of C or C++ code, for looking up a value depending on the input string. The hash function is perfect, which means that the hash table has no collisions, and the hash table lookup needs a single string comparison only. GNU gperf is highly customizable. There are options for generating C or C++ code, for emitting switch statements or nested ifs instead of a hash table, and for tuning the algorithm employed by gperf.