LIBXO(3)

NAME
xo_open_marker, xo_open_marker_h, xo_close_marker, xo_close_marker_h - prevent and allow closing of open constructs

LIBRARY
libxo

SYNOPSIS
#include <libxo/xo.h>
xo_ssize_t
xo_open_marker(const char *name);
xo_ssize_t
xo_open_marker_h(xo_handle_t *handle, const char *name);
xo_ssize_t
xo_close_marker(const char *name);
xo_ssize_t
xo_close_marker_h(xo_handle_t *handle, const char *name);

DESCRIPTION
libxo represents hierarchy using two constructs: “containers” and “lists”. A marker can be used to affect how open constructs are closed, either by preventing their (implicit or explicit) closure or by forcing their closure. While a marker is open, no other open constructs can be closed. When a marker is closed, all constructs open since the marker was opened will be closed. A marker is used to "freeze" any open constructs. Calls to xo_close_*() functions that would normally close them will be ignored, effectively blocking their closure. However when xo_close_marker() is called, any containers, lists, or leaf-lists open since the matching xo_open_marker() call will be close and the marker discarded. Markers use names which are not user-visible, allowing the caller to choose appropriate internal names. The marker has no value and is not emitted in any form.

To open a marker, call xo_open_marker() or xo_open_marker_h(). The former uses the default handle and the latter accepts a specific handle.

To close a marker, use the xo_close_marker() or xo_close_marker_h() functions.

Each open call must have a matching close call.

In this example, the xo_close_container() call on line [1] will be ignored, since the open marker "outer" will prevent close of any open constructs that precede it. The xo_close_marker() call on line [2] will close the "system" container, since it was opened after the "outer" marker.
        Example:
            xo_open_container("top");
    	xo_open_marker("outer");
            xo_open_container("system");
            xo_emit("{:host-name/%s%s%s", hostname,
                    domainname ? "." : "", domainname ?: "");
            xo_close_container("top");   /* [1] */
    	xo_close_marker("outer");    /* [2] */
            xo_close_container("top");

In this example, the code whiffles through a list of fish, calling a function to emit details about each fish. The marker "fish-guts" is used to ensure that any constructs opened by the function are closed properly.

        for (i = 0; fish[i]; i++) {
            xo_open_instance("fish");
            xo_open_marker("fish-guts");
            dump_fish_details(i);
            xo_close_marker("fish-guts");
        }

SEE ALSO
xo_emit(3), libxo(3)

HISTORY
The libxo library first appeared in FreeBSD 11.0.

AUTHORS
libxo was written by Phil Shafer <phil@freebsd.org>.