liushuyu/portmidi

PortMIDI is a library that lets software communicate with MIDI devices, things like electronic keyboards, drum pads, synthesizers, and other musical gear. If you're building a music app and need it to receive notes from a piano keyboard or send commands to a synthesizer, this library handles that connection for you. At a technical level, it provides a consistent interface across Windows, Mac, and Linux so that a music program doesn't need completely different code for each operating system. You open a MIDI port (which represents a connected device), and then you can read incoming MIDI messages or write outgoing ones. The library manages the state of each open device using pointers rather than simple index numbers, which mirrors the design of a similar audio library called PortAudio. The README spends a lot of time on error handling, which turned out to be more complicated than the author expected. Functions return error codes that you can check, and when errors are system-specific, there's a way to retrieve a text description of what went wrong. Errors that happen during background MIDI input are handled differently depending on the platform, Mac OS X deals with them in callbacks, while Windows apparently has very few asynchronous errors to worry about. There's also a debug mode for research-oriented console applications that prints error messages and halts the program, though this isn't suitable for production apps where you'd want to recover gracefully. This library is meant for developers building music software, digital audio workstations, notation programs, live performance tools, or music education apps. It's written in C, with some community-contributed support for Common Lisp and C#. The README doesn't go into much detail on setup or usage beyond pointing to platform-specific documentation files and the main header file for API reference.