Unix Qt 5.6 QSettings 找不到 QSettings::SystemScope 配置文件

Question

Link 到 Qt 错误报告：QTBUG-53313

从 Qt 5.5 迁移到 Qt 5.6 会出现 QSettings 问题，它无法在系统范围内找到 QSettings 配置文件。在下面的main.cpp中，QSettings被各种方式初始化，然后查询它的属性：

// File: main.cpp

#include <QApplication>
#include <QDebug>
#include <QSettings>
#include <QCoreApplication>

#define ASSUMED_SYSTEM_CONFIG "/etc/xdg/TheOrg/TheApp.conf"
#define ASSUMED_USER_CONFIG "/home/user/.config/TheOrg/TheApp.conf"

void print_info(const QSettings& settings, const char& use_case);

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QCoreApplication::setOrganizationName("TheOrg");
    QCoreApplication::setApplicationName("TheApp");

    QSettings settings_a;
    QSettings settings_b("TheOrg", "TheApp");
    QSettings settings_c(QSettings::SystemScope, "TheOrg", "TheApp");
    QSettings settings_d(QSettings::NativeFormat, QSettings::SystemScope, "TheOrg", "TheApp");

    print_info(settings_a, 'a');    
    print_info(settings_b, 'b');    
    print_info(settings_c, 'c');    
    print_info(settings_d, 'd');

    return a.exec();
}

void print_info(const QSettings& settings, const char& use_case)
{
    int value = settings.value("the_value").toInt();

    qDebug() << "Using case (" << use_case << ")";

    qDebug() << "The value is " << value;

    qDebug() << "Settings scope is: " << ((settings.scope() == QSettings::SystemScope) ? "System" : "User");
    qDebug() << "Settings organization is: " << settings.organizationName();
    qDebug() << "Settings application name is: " << settings.applicationName();
    qDebug() << "Settings fallbackEnabled is: " << settings.fallbacksEnabled();
    qDebug() << "Settings filename is: " << settings.fileName() << "\n";
}

系统上ASSUMED_USER_CONFIG文件不存在。

ASSUMED_SYSTEM_CONFIG 文件 在系统上确实存在 并且包含：

the_value = 42

用Qt 5.5编译，程序returns:

Using case ( a )
The value is  42
Settings scope is:  User
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/.config/TheOrg/TheApp.conf" 

Using case ( b )
The value is  42
Settings scope is:  User
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/.config/TheOrg/TheApp.conf" 

Using case ( c )
The value is  42
Settings scope is:  System
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/etc/xdg/TheOrg/TheApp.conf" 

Using case ( d )
The value is  42
Settings scope is:  System
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/etc/xdg/TheOrg/TheApp.conf"

用Qt 5.6编译，程序returns:

Using case ( a )
The value is  0
Settings scope is:  User
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/.config/TheOrg/TheApp.conf" 

Using case ( b )
The value is  0
Settings scope is:  User
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/.config/TheOrg/TheApp.conf" 

Using case ( c )
The value is  0
Settings scope is:  System
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/Qt5.6/5.6/gcc_64/etc/xdg/TheOrg/TheApp.conf" 

Using case ( d )
The value is  0
Settings scope is:  System
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/Qt5.6/5.6/gcc_64/etc/xdg/TheOrg/TheApp.conf"

这里有几个问题：

当使用 Qt 5.5 编译时，设置 'filename' 正在按所有情况 (a、b、c、d) 的预期构建。案例 'a' 和 'b' 是 falling back 到 ASSUMED_SYSTEM_CONFIG 文件，因为 ASSUMED_USER_CONFIG 文件不存在。因此，从设置文件中正确检索 'the_value'。

然而，当使用 Qt 5.6 编译时，'filename' 的设置似乎在 'c' 和 'd' 的情况下构建不正确（正确的路径被附加到“/home/user/Qt5.6/5.6/gcc_64").因此，无法从设置文件中检索 'the_value'。

我没有覆盖 Qt Creator 中的任何默认环境变量，Qt 5.6 是由 Qt 维护工具自动安装的。我知道我可以使用环境变量 XDG_CONFIG_HOME 来设置 QSettings::SystemScope 文件的绝对路径，但我认为我不必这样做。

重申主要问题，我如何将 ASSUMED_SYSTEM_CONFIG 文件（即 QSettings::SystemScope）与 QSettings 一起使用？

还有其他人反对吗？我已经在两台不同的机器上测试过了。

Answer 1

这是预编译 linux 二进制文件的问题。如果您从源代码编译 Qt 5.6，则可以通过使用标志 '-sysconfdir=/etc' 编译 Qt 来避免此问题。

如果这不是一个选项，您可以设置环境变量，XDG_CONFIG_HOME。

This bug should now be fixed in the Qt 5.6.1 snapshot。

Unix Qt 5.6 QSettings 找不到 QSettings::SystemScope 配置文件

Unix Qt 5.6 QSettings cannot find QSettings::SystemScope configuration file

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