= nng_listener_id(3)
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//
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// Copyright 2018 Staysail Systems, Inc. <info@staysail.tech>
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// Copyright 2018 Capitar IT Group BV <info@capitar.com>
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//
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// This document is supplied under the terms of the MIT License, a
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// copy of which should be located in the distribution where this
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// file was obtained (LICENSE.txt). A copy of the license may also be
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// found online at https://opensource.org/licenses/MIT.
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//
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== NAME
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nng_listener_id - return numeric listener identifier
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== SYNOPSIS
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[source, c]
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----
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#include <nng/nng.h>
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int nng_listener_id(nng_listener l);
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----
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== DESCRIPTION
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The `nng_listener_id()` function returns a positive identifier for the
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listener _l_, if it is valid.
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Otherwise it returns `-1`.
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NOTE: A listener is considered valid if it was ever created with the
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xref:nng_listener_create.3.adoc[`nng_listener_create()`] or
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xref:nng_listen.3.adoc[`nng_listen()`] functions.
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listeners that are allocated on the stack or statically should be
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initialized with the macro
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xref:nng_ctx.5.adoc#NNG_LISTENER_INITIALIZER[`NNG_LISTENER_INITIALIZER`] to ensure that
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they cannot be confused with a valid listener before they are created properly.
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== RETURN VALUES
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This function returns the positive value for the listener identifier, or
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`-1` if the listener is invalid.
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== ERRORS
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None.
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== SEE ALSO
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[.text-left]
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xref:nng_listener.5.adoc[nng_listener(5)],
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xref:nng.7.adoc[nng(7)]
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