This is the complete documentation of the public API made available to users of libgpiod.

The API is logically split into several sections. For each opaque data class, there's a set of functions for manipulating it. Together they can be thought of as objects and their methods in OOP parlance.

General note on error handling: all functions exported by libgpiod that can fail, set errno to one of the error values defined in errno.h upon failure. The way of notifying the caller that an error occurred varies between functions, but in general a function that returns an int, returns -1 on error, while a function returning a pointer indicates an error condition by returning a NULL pointer. It's not practical to list all possible error codes for every function as they propagate errors from the underlying libc functions.

In general libgpiod functions are NULL-aware. For functions that are logically methods of data classes - ones that take a pointer to the object of that class as the first argument - passing a NULL pointer will result in the program aborting the execution. For non-methods, init functions and methods that take a pointer as any of the subsequent arguments, the handling of a NULL-pointer depends on the implementation and may range from gracefully handling it, ignoring it or returning an error.