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2ec660b2ea
The C standard does not specify whether the underlying type of an enum
is signed or unsigned, and until C23 there was no way to control this
explicitly. GCC appears to make enums unsigned unless there is a
negative value among cases of the enum, in which case it becomes signed.
MSCV appears to make enums signed by default.
A bitfield of an enum type (which is not specificied in the C standard
either) behaves as if it was an instance of a numeric type with a
reduced value range. Specifically, a 'signed int val : 2;' bitfield will
have the possible values of -2, -1, 0, and 1, with the usual wraparound
behavior for the values that don't fit (although this too is
implementation-defined).
This causes the following issue, if we have:
typedef enum
{
G_ZERO,
G_ONE,
G_TWO
} GFoo;
struct _GBar
{
GFoo foo : 2;
};
and then assign bar.foo = G_TWO and read it back, it will have the
expected value of 2 (aka G_TWO) on GCC, but a value of -2 (not matching
any of the enum variants) on MSVC.
There does not seem to be any way to influence signedness of an enum
prior to C23, nor is there a 'unsigned GFoo foo : 2;' syntax. The only
remaining options seems to be never using enums in bitfields, which is
what this change implements.
This corresponds to https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/6467
in GTK.
Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
94 lines
4.3 KiB
C
94 lines
4.3 KiB
C
/* GIO - GLib Input, Output and Streaming Library
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*
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* Copyright (C) 2006-2007 Red Hat, Inc.
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*
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* SPDX-License-Identifier: LGPL-2.1-or-later
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General
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* Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
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*
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* Author: Alexander Larsson <alexl@redhat.com>
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*/
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#ifndef __G_FILE_ATTRIBUTE_PRIV_H__
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#define __G_FILE_ATTRIBUTE_PRIV_H__
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#include "gfileattribute.h"
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#include "gfileinfo.h"
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#define G_FILE_ATTRIBUTE_VALUE_INIT {0}
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typedef struct {
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guint type : 8; /* GFileAttributeType */
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guint status : 8; /* GFileAttributeStatus */
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union {
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gboolean boolean;
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gint32 int32;
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guint32 uint32;
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gint64 int64;
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guint64 uint64;
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char *string;
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GObject *obj;
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char **stringv;
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} u;
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} GFileAttributeValue;
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GFileAttributeValue *_g_file_attribute_value_new (void);
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void _g_file_attribute_value_free (GFileAttributeValue *attr);
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void _g_file_attribute_value_clear (GFileAttributeValue *attr);
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void _g_file_attribute_value_set (GFileAttributeValue *attr,
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const GFileAttributeValue *new_value);
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GFileAttributeValue *_g_file_attribute_value_dup (const GFileAttributeValue *other);
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gpointer _g_file_attribute_value_peek_as_pointer (GFileAttributeValue *attr);
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char * _g_file_attribute_value_as_string (const GFileAttributeValue *attr);
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const char * _g_file_attribute_value_get_string (const GFileAttributeValue *attr);
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const char * _g_file_attribute_value_get_byte_string (const GFileAttributeValue *attr);
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gboolean _g_file_attribute_value_get_boolean (const GFileAttributeValue *attr);
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guint32 _g_file_attribute_value_get_uint32 (const GFileAttributeValue *attr);
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gint32 _g_file_attribute_value_get_int32 (const GFileAttributeValue *attr);
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guint64 _g_file_attribute_value_get_uint64 (const GFileAttributeValue *attr);
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gint64 _g_file_attribute_value_get_int64 (const GFileAttributeValue *attr);
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GObject * _g_file_attribute_value_get_object (const GFileAttributeValue *attr);
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char ** _g_file_attribute_value_get_stringv (const GFileAttributeValue *attr);
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void _g_file_attribute_value_set_from_pointer(GFileAttributeValue *attr,
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GFileAttributeType type,
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gpointer value_p,
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gboolean dup);
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void _g_file_attribute_value_set_string (GFileAttributeValue *attr,
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const char *string);
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void _g_file_attribute_value_set_byte_string (GFileAttributeValue *attr,
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const char *string);
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void _g_file_attribute_value_set_boolean (GFileAttributeValue *attr,
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gboolean value);
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void _g_file_attribute_value_set_uint32 (GFileAttributeValue *attr,
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guint32 value);
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void _g_file_attribute_value_set_int32 (GFileAttributeValue *attr,
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gint32 value);
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void _g_file_attribute_value_set_uint64 (GFileAttributeValue *attr,
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guint64 value);
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void _g_file_attribute_value_set_int64 (GFileAttributeValue *attr,
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gint64 value);
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void _g_file_attribute_value_set_object (GFileAttributeValue *attr,
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GObject *obj);
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void _g_file_attribute_value_set_stringv (GFileAttributeValue *attr,
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char **value);
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GFileAttributeValue *_g_file_info_get_attribute_value (GFileInfo *info,
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const char *attribute);
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#endif /* __G_FILE_ATTRIBUTE_PRIV_H__ */
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