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   sd_bus_message_exit_container    ( 3 )

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Имя (Name)

sd_bus_message_open_container, sd_bus_message_close_container,
       sd_bus_message_enter_container, sd_bus_message_exit_container -
       Create and move between containers in D-Bus messages

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Синопсис (Synopsis)

#include <systemd/sd-bus.h>

       int sd_bus_message_open_container(sd_bus_message *m, char type,
                                         const char *contents);

       int sd_bus_message_close_container(sd_bus_message *m);

       int sd_bus_message_enter_container(sd_bus_message *m, char type,
                                          const char *contents);

       int sd_bus_message_exit_container(sd_bus_message *m);

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Описание (Description)

sd_bus_message_open_container() appends a new container to the
       message m. After opening a new container, it can be filled with
       content using sd_bus_message_append(3) and similar functions.
       Containers behave like a stack. To nest containers inside each
       other, call sd_bus_message_open_container() multiple times
       without calling sd_bus_message_close_container() in between. Each
       container will be nested inside the previous container.  type
       represents the container type and should be one of "r", "a", "v"
       or "e" as described in sd_bus_message_append(3). Instead of
       literals, the corresponding constants SD_BUS_TYPE_STRUCT,
       SD_BUS_TYPE_ARRAY, SD_BUS_TYPE_VARIANT or SD_BUS_TYPE_DICT_ENTRY
       can also be used.  contents describes the type of the container's
       elements and should be a D-Bus type string following the rules
       described in sd_bus_message_append(3).

       sd_bus_message_close_container() closes the last container opened
       with sd_bus_message_open_container(). On success, the write
       pointer of the message m is positioned after the closed container
       in its parent container or in m itself if there is no parent
       container.

       sd_bus_message_enter_container() enters the next container of the
       message m for reading. It behaves mostly the same as
       sd_bus_message_open_container(). Entering a container allows
       reading its contents with sd_bus_message_read(3) and similar
       functions.  type and contents are the same as in
       sd_bus_message_open_container().

       sd_bus_message_exit_container() exits the scope of the last
       container entered with sd_bus_message_enter_container(). It
       behaves mostly the same as sd_bus_message_close_container(). Note
       that sd_bus_message_exit_container() may only be called after
       iterating through all members of the container, i.e. reading or
       skipping them. Use sd_bus_message_skip(3) to skip over felds of a
       container in order to be able to exit the container with
       sd_bus_message_exit_container() without reading all members.

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Возвращаемое значение (Return value)

On success, these functions return a non-negative integer.
       sd_bus_message_open_container() and
       sd_bus_message_close_container() return 0.
       sd_bus_message_enter_container() returns 1 if it successfully
       opened a new container, and 0 if that was not possible because
       the end of the currently open container or message was reached.
       sd_bus_message_exit_container() returns 1 on success. On failure,
       all of these functions return a negative errno-style error code.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           m or contents are NULL or type is invalid.

       -EPERM
           The message m is already sealed.

       -ESTALE
           The message m is in an invalid state.

       -ENOMEM
           Memory allocation failed.

       -EBUSY
           sd_bus_message_exit_container() was called but there are
           unread members left in the container.

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Примечание (Note)

These APIs are implemented as a shared library, which can be
       compiled and linked to with the libsystemd pkg-config(1) file.

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Примеры (Examples)

Example 1. Append an array of strings to a message

           #include <systemd/sd-bus.h>

           int append_strings_to_message(sd_bus_message *m, const char *const *arr) {
             int r;

             r = sd_bus_message_open_container(m, 'a', "s");
             if (r < 0)
               return r;

             for (const char *s = *arr; *s; s++) {
               r = sd_bus_message_append(m, "s", s);
               if (r < 0)
                 return r;
             }

             return sd_bus_message_close_container(m);
           }

       Example 2. Read an array of strings from a message

           #include <stdio.h>

           #include <systemd/sd-bus.h>

           int read_strings_from_message(sd_bus_message *m) {
             int r;

             r = sd_bus_message_enter_container(m, 'a', "s");
             if (r < 0)
               return r;

             for (;;) {
               const char *s;

               r = sd_bus_message_read(m, "s", &s);
               if (r < 0)
                 return r;
               if (r == 0)
                 break;

               printf("%s\n", s);
             }

             return sd_bus_message_exit_container(m);
           }

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Смотри также (See also)

systemd(1), sd-bus(3), sd_bus_message_append(3),
       sd_bus_message_read(3), sd_bus_message_skip(3), The D-Bus
       specification[1]

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Примечание (Note)

1. The D-Bus specification
           https://dbus.freedesktop.org/doc/dbus-specification.html

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