11. ISO C99 Implementation of Base64

RFC 4648 includes an ISO C99 implementation of Base64 to illustrate the algorithm. The code is an example, not the only valid implementation.

The example demonstrates alphabet lookup, padding generation, and decoder validation. Implementers should still review boundary checks, allocation behavior, error reporting, and handling of non-alphabet characters for their own environment.

In security-sensitive software, malformed padding, invalid characters, and non-zero pad bits should be handled according to the referring specification and should not be silently accepted by default.