## nn_errno

Return most recent error (compatible API).

### Synopsis

```c
#include <nanomsg/nn.h>

int nn_errno(void);
```

### Description

The `nn_errno` function returns the error number corresponding to the
most recent failed operation by the calling thread.

IMPORTANT: The error numbers returned from this function includes errors caused by system functions, which overlap the usual `errno` variable.
However, the values returned may include numeric values that are not defined by the system, but are unique to _libnanomsg_.

This library implements the following error numbers, in addition to any others that might be set for `errno` by the underlying system:

### Return Values

This function returns the value of `errno`.
If no operation has failed, then this will be zero.

### Errors

[horizontal]
`EINTR`:: Operation interrupted.
`ENOMEM`:: Insufficient memory.
`EINVAL`:: Invalid argument.
`EBUSY`:: Resource is busy.
`ETIMEDOUT`:: Operation timed out.
`ECONNREFUSED`:: Connection refused by peer.
`EBADF`:: Invalid or closed socket.
`EAGAIN`:: Operation would block.
`ENOTSUP`:: Protocol or option not supported.
`EADDRINUSE`:: Requested address is already in use.
`EFSM`:: Protocol state incorrect.
`EPROTO`:: Protocol error.
`EHOSTUNREACH`:: Remote peer is unreachable.
`EADDRNOTAVAIL`:: Requested address is not available.
`EACCES`:: Permission denied.
`EMSGSIZE`:: Message is too large.
`ECONNABORTED`:: Connection attempt aborted.
`ECONNRESET`:: Connection reset by peer.
`EEXIST`:: Resource already exists.
`EMFILE`:: Too many open files.
`ENOSPC`:: Insufficient persistent storage.

### See Also

xref:nn_strerror.adoc[nn_strerror]
