# Error codes

The library uses integer values to specify error codes inside of its context. These integer return codes are defined in `akerror.h` in the form of `AKERR_xxxxx` where `xxxxx` is the name of the error code in question. See `akerror.h` for a list of defined errors and their descriptions. 

You can define additional error types as integer constants. Values 0 through 255
are reserved by libakerror (the host's errno values plus the `AKERR_*` codes);
consumers allocate codes starting at `AKERR_FIRST_CONSUMER_STATUS` (256). Status
names are stored sparsely, so any `int` is a legal status and no compile
definition is needed to use large values. Note that no consumer status can be a
process exit code — see [Exit status](exit-status.md).

Every library that may coexist in one process must reserve its range during
initialization. `akerr_reserve_status_range()` and
`akerr_register_status_name()` report failure the way everything else in this
library does — they return `akerr_ErrorContext *`, and they are marked
`AKERR_NOIGNORE` — so a collision is an exception you can `CATCH`, `HANDLE`, or
`PASS` up out of your initialization:

```c
#define MYLIB_OWNER "my-library"

akerr_ErrorContext AKERR_NOIGNORE *mylib_init(void)
{
    PREPARE_ERROR(errctx);

    /* Another component owning part of the range propagates to our caller. */
    PASS(errctx, akerr_reserve_status_range(256, 16, MYLIB_OWNER));

    /* Then name each code, quoting the owner you reserved with. */
    PASS(errctx, akerr_register_status_name(MYLIB_OWNER, 256,
                                            "Some Error Code Description"));
    SUCCEED_RETURN(errctx);
}
```

Reservations are process-local, fixed-capacity, and idempotent when the same
owner repeats the exact same range. They preserve compile-time integer constants
so `HANDLE` still works, since `case` labels require them.

Naming a status outside your reservation raises `AKERR_STATUS_NAME_FOREIGN`, and
naming one nobody reserved raises `AKERR_STATUS_NAME_UNRESERVED`; a colliding
reservation raises `AKERR_STATUS_RANGE_OVERLAP`, with a message naming the real
owner. See [UPGRADING.md](../UPGRADING.md) for the full list of statuses these two
functions raise, the capacity limits and how to raise them, and thread-safety
rules.