获取 GVariant 的内容

Posted 2023-04-14

【中文标题】获取 GVariant 的内容

【英文标题】：Get the contents of GVariant

【发布时间】：2018-03-25 09:40:07

【问题描述】：

我目前正在尝试与 dbus 通信并有一个函数，它将返回 array of struct(string, uint32, string, string, object path)。我将结果存储在GVariant 中，打印此GVariant 表明那里有正确的结果值。

更具描述性：我尝试获取 Systemd 的 Logind Managers ListSessions 的结果。

print的输出是：

[('2', uint32 1000, 'nidhoegger', 'seat0', objectpath
'/org/freedesktop/login1/session/_32'), ('6', 1001, 'test', 'seat0',
'/org/freedesktop/login1/session/_36'), ('c2', 111, 'lightdm',
'seat0', '/org/freedesktop/login1/session/c2')]

我现在正在尝试使用以下方法在循环中获取每个数组元素：

for (uint32_t i = 0; i < ::g_variant_n_children(v); ++i)

    GVariant *child = ::g_variant_get_child_value(v, i);

打印我得到的孩子时：

<('2', uint32 1000, 'nidhoegger', 'seat0', objectpath '/org/freedesktop/login1/session/_32')>

到目前为止一切顺利。现在我正在尝试以这种方式使用g_variant_get 获取单个项目：

gchar *id = NULL;
uint32_t uid = 0;
gchar *user = NULL;
gchar *seat = NULL;
gchar *session_path = NULL;

::g_variant_get(v, "(susso)", &id, &uid, &user, &seat, &session_path);

但它只给了我这个断言：

(process:12712): GLib-CRITICAL **: the GVariant format string '(susso)' has a type of '(susso)' but the given value has a type of 'v'

(process:12712): GLib-CRITICAL **: g_variant_get_va: assertion 'valid_format_string (format_string, !endptr, value)' failed

如果这是相关的：我生成了与gdbus-codegen 通信的代码，并且获取值的函数具有此签名：

gboolean login1_manager_call_list_sessions_sync (
    Login1Manager *proxy,
    GVariant **out_unnamed_arg0,
    GCancellable *cancellable,
    GError **error);

我做错了什么？为什么它返回“v”作为值？

【参考方案1】：

::g_variant_get(v, "(susso)", &id, &uid, &user, &seat, &session_path);

这看起来很可疑。你应该打电话给child，而不是v。

以下 C 代码对我来说很好用：

/* gcc `pkg-config --cflags --libs glib-2.0` -o test test.c */
#include <glib.h>

int
main (void)

  g_autoptr(GVariant) sessions = NULL;

  sessions = g_variant_new_parsed ("[('2', uint32 1000, 'nidhoegger', 'seat0', objectpath '/org/freedesktop/login1/session/_32'), ('6', 1001, 'test', 'seat0', '/org/freedesktop/login1/session/_36'), ('c2', 111, 'lightdm', 'seat0', '/org/freedesktop/login1/session/c2')]");

  for (gsize i = 0; i < g_variant_n_children (sessions); i++)
    
      g_autoptr(GVariant) child = g_variant_get_child_value (sessions, i);
      g_message ("Child %" G_GSIZE_FORMAT ": %s", i, g_variant_get_type_string (child));

      guint32 uid;
      const gchar *id, *user, *seat, *session_path;

      g_variant_get (child, "(&su&s&s&o)", &id, &uid, &user, &seat, &session_path);

      g_message ("%s, %u, %s, %s, %s", id, uid, user, seat, session_path);
    

  return 0;

它打印以下内容：

** Message: Child 0: (susso)
** Message: 2, 1000, nidhoegger, seat0, /org/freedesktop/login1/session/_32
** Message: Child 1: (susso)
** Message: 6, 1001, test, seat0, /org/freedesktop/login1/session/_36
** Message: Child 2: (susso)
** Message: c2, 111, lightdm, seat0, /org/freedesktop/login1/session/c2