In .Net you typically have an app.config file and built in ways to access the configuration.
Is there an equivalent standard approach to configuration using Qt?
For example, lets say my application connects to an online server, I want the ability to store the connection details (user defined).
Is this a case of "roll your own", or is there a way to store and read these configurations using XML, or any other format with easy read/write methods provided by Qt?
Edit: To add some complication to the question. This is a Linux console app, so looking specifically for file based and transparent config please.
You could use QSettings for this. Please refer to the documentation for details:
http://qt-project.org/doc/qt-5.1/qtcore/qsettings.html
You could always use other formats as well like XML, Json, and so forth, but generically speaking, QSettings is the way, or if you are writing a KDE application, then probably KConfig.
These are the two important methods you need to be aware of when dealing with QSettings for reading and writing:
Reading
QVariant QSettings::value(const QString & key,
const QVariant & defaultValue = QVariant()) const
Writing
void QSettings::setValue(const QString & key, const QVariant & value)
Then, you can simply stick to the native format (or even ini on your Linux if you prefer):
QSettings::NativeFormat 0 Store the settings using the most
appropriate storage format for the platform. On Windows, this means
the system registry; on Mac OS X, this means the CFPreferences API; on
Unix, this means textual configuration files in INI format.
Here you can find an example for your convenience:
#include <QSettings>
int main()
{
....
QSettings settings("Foo", "Bar");
// settings.beginGroup("application");
QString string = settings.value("foo", "bar");
// settings.endGroup();
....
}
Note, the groups are optional, and it depends on your exact purpose. You can group settings that way to keep certain ones encapsulated.
This may also be important for you to know as per documentation:
On Unix systems, if the file format is NativeFormat, the following files are used by default:
$HOME/.config/MySoft/Star Runner.conf (Qt for Embedded Linux: $HOME/Settings/MySoft/Star Runner.conf)
$HOME/.config/MySoft.conf (Qt for Embedded Linux: $HOME/Settings/MySoft.conf)
/etc/xdg/MySoft/Star Runner.conf
/etc/xdg/MySoft.conf
Related
My program needs to read/write a text (just a few lines) file with its settings to disk. To specify a path in code may work well on one platform, like windows, but if runs it on Linux, the path is not cross platform.
I am looking for a similar solution to QSettings that saves settings to different paths or has its native ways to handle this. Programmers don't need to do with the details. But the text file is not suitable to be saved as a value in QSettings.
No user interaction should be needed to obtain such path. The text file should persist across application restarts. It can't be a temporary file.
Is there an existing solution in Qt and what is the API that should be used?
The location of application-specific settings storage differs across platforms. Qt 5 provides a sensible solution via QStandardPaths.
Generally, you'd store per-user settings in QStandardPaths::writableLocation(QStandardPaths::AppDataLocation). If you wish the settings not to persist in the user's roaming profile on Windows, you can use QStandardPaths::AppLocalDataLocation, it has the meaning of AppDataLocation on non-Windows platforms.
Before you can use the standard paths, you must set your application name via QCoreApplication::setApplicationName, and your organization's name using setOrganizationName or setOrganizationDomain. The path will depend on these, so make sure they are unique for you. If you ever change them, you'll lose access to old settings, so make sure you stick with name and domain that makes sense for you.
The path is not guaranteed to exist. If it doesn't, you must create it yourself, e.g. using QDir::mkpath.
int main(int argc, char ** argv) {
QApplication app{argc, argv};
app.setOrganizationDomain("stackoverflow.com");
app.setApplicationName("Q32525196.A32535544");
auto path = QStandardPaths::writableLocation(QStandardPaths::AppDataLocation);
if (path.isEmpty()) qFatal("Cannot determine settings storage location");
QDir d{path};
if (d.mkpath(d.absolutePath()) && QDir::setCurrentPath(d.absolutePath())) {
qDebug() << "settings in" << QDir::currentPath();
QFile f{"settings.txt"};
if (f.open(QIODevice::WriteOnly | QIODevice::Truncate))
f.write("Hello, World");
}
}
If you want to save some user related data, you can get user home directory path using QDir::homePath().
There is QDir to handle paths to dirs, QFileInfo for platform independent file information and QDir's homePath()
My proposal is to use these classes and use QDir::home() or QDir::homePath() to find a directory where to write to, since the user has write permissions in his homedir and it exists on each platform.
You can store file in application directory. Take a look at QCoreApplication::applicationDirPath().
From Qt documentation:
Returns the directory that contains the application executable.
I'm an unfortunate beginner at C++ and using the Qt GUI designer program seemed perfect for my needs, except I'm having problems trying to write out the code necessary for this. I could use the QSettings string to store local settings on the hard drive, but I personally hate it when programs do the %HOME_LOCAL%\APPS_SETTINGS bull that some do. I need to save a text file for both settings and a local\host database, within the program directory, to remember strings to read from later.
What is the line of code I need to make use of a local host text database or is there a better option? And how can I store that with the local program inside its directory?
You can use QSettings with any file, with constructor QSettings::QSettings ( const QString & fileName, Format format, QObject * parent = 0 ).
To get the program directory, you can use QCoreApplication::applicationDirPath().
So, answer to your question, statement to put after creation of QApplication instance:
QSettings *settings = new QSettings(
QCoreApplication::applicationDirPath() + "/settings.ini",
QSettings::IniFormat,
qApp);
But, as noted in the comments under question, if you're making your program for general distribution, you should use the OS default. Examine all the constructors of QSettings to see what it can do. User does not often have write permission in the application directory. Note that you can also store settings to Windows registry with QSettings::NativeFormat.
In the simplest possible terms (I'm an occasional programmer who lacks up-to-date detailed programming knowledge) can someone explain the simplest way to make use of the registry in codegear C++ (2007).
I have a line of code in an old (OLD!) program I wrote which is causing a significant delay in startup...
DLB->Directory=pIniFile->ReadString("Options","Last Directory","no key!");
The code is making use of an ini file. I would like to be able to use the registry instead (to write variables such as the last directory the application was using)
But the specifics are not important. I'd just like a generic how-to about using the registry that's specific to codegear c++ builder.
I've googled this, but as usual with this type of thing I get lots of pages about c++ builder and a few pages about the windows registry, but no pages that explain how to use one with the other.
Use the TRegistry class... (include registry.hpp)
//Untested, but something like...
TRegistry *reg = new TRegistry;
reg->RootKey = HKEY_CURRENT_USER; // Or whatever root you want to use
reg->OpenKey("theKey",true);
reg->ReadString("theParam",defaultValue);
reg->CloseKey();
Note, opening and reading a ini file is usually pretty fast, so maybe you need to test your assumption that the reading of the ini is actually your problem, I don't think that just grabbing your directory name from the registry instead is going to fix your problem.
Include the Registry.hpp file:
#include <Registry.hpp>
Then in any function you have, you can write the following to read the value:
String __fastcall ReadRegistryString(const String &key, const String &name,
const String &def)
{
TRegistry *reg = new TRegistry();
String result;
try {
reg->RootKey = HKEY_CURRENT_USER;
if (reg->OpenKeyReadOnly(key)) {
result = reg->ReadString(name, def);
reg->CloseKey();
}
}
__finally {
delete reg;
}
return result;
}
So reading the value should be as easy as:
ShowMessage(ReadRegistryString("Options", "Last Directory", "none"));
You can use the following to write the value:
void __fastcall WriteRegistryString(const String &key, const String &name,
const String &value)
{
TRegistry *reg = new TRegistry();
try {
reg->RootKey = HKEY_CURRENT_USER;
if (reg->OpenKey(key, true)) {
reg->WriteString(name, value);
reg->CloseKey();
}
}
__finally {
delete reg;
}
}
Should be self explaining, remembering the try ... finally is actually really helpful when using the VCL TRegistry class.
Edit
I've heard that .ini files are stored in the registry in Windows, so if you want the speed advantage of ini files you should call them something else - like .cfg
This is something I've heard from an although reliable source, I haven't tested it myself.
Tim is right but an even simpler class to use is TIniRegFile but it is also more limited in what you can do.
Please see the documentation for the QSettings class from the Qt 4.5 library. It will allow you to load and store your program's configuration settings easily and in a cross-platform manner. The Windows implementation uses the Windows registry for loading and storing your program's configuration data. On other platforms, the platform's preferred, native mechanism for storing configuration data will be used. This is far better than interacting with the Windows registry directly, as you will not be tied to a specific platform.
linux: $HOME/.config
windows: %APPDATA%
mac os: $HOME/.config
It can be set using http://qt-project.org/doc/qt-4.8/qsettings.html#setPath, but it seems as I am not able to retrieve it.
http://qt-project.org/doc/qt-4.8/qlibraryinfo.html#location QLibraryInfo::LibrariesPath returns the system wide settings dir, which is not what I want.
Any ideas, or do I have to code it separately for each platform?
€: I want to create a sub directory, and store files into it. (You may punish me if this is a bad idea)
This might not answer your question directly: if you want to store per-user persistent data, shouldn't you use QDesktopServices::storageLocation(QDesktopServices::DataLocation) instead?
This is a nasty workaround. First you create QSettings, then get its location.
QSettings cfg(QSettings::IniFormat, QSettings::UserScope,
"organization", "application");
QString config_dir = QFileInfo(cfg.fileName()).absolutePath() + "/";
Credits go to the Qt Centre forum.
QSettings stores the default config in the user AppData directory. See documentation for QSettings. Also this code instructs to store the config in the Ini file format.
this works on both qt 4 and qt 5
QApplication::setApplicationName("MyApp");
QApplication::setOrganizationName("Me");
QString homePath;
#if QT_VERSION >= 0x050000
homePath = QStandardPaths::writableLocation(QStandardPaths::DataLocation);
#else
homePath = QDesktopServices::storageLocation(QDesktopServices::DataLocation);
#endif
Why do you need to know the settings path? If you are going to put settings in it, you could use QSettings. I could see making a subdirectory to hold various settings, but it seems like the easiest way would be to use QSettings directly.
As far as I can tell, you can't retrieve the path. In the Qt source, src/corelib/io/qsettings.cpp, there is a function to get the path:
static QString getPath(QSettings::Format format, QSettings::Scope scope)
{
...
but it's not accessible from code using Qt. You can't copy it and use it either, because it uses internal Qt globals to store the path...
EDIT: A solution was posted, using QDesktopServices.storageLocation(QDesktopServices.DataLocation) but it doesn't do exactly what the question was asking for, i.e. if I set a custom path using QSettings.setPath() it doesn't reflect the change.
What platform are you at?
Might be related or not but in windows, the default is to write QSettings to the registry.
I read more into the question than there was as it was originally posted. It is clearer after the edits. Ok, so can't you use..
QString QSettings::fileName () const
Returns the path where settings are written to using this QSettings object are stored.
On Windows, if the format is QSettings::NativeFormat, the return value is a system registry path, not a file path.
What is a fairly standard way for storing application settings, mainly for windows but also easy to move over to other platforms.
There's basically 4 groups of settings I want to have:
Global settings, affects all users, and may be moved between machines
Global system settings, affects all users, but specific to that system (eg defaults for that system, eg graphics options)
User settings, user settings that are moved between systems (eg sound volume)
User system settings, user settings specific to that system (eg graphics options that are hardware dependent)
Each level overrides the previous level, allowing for "global settings" to be largly the applications defaults, with user settings storing the options the user chose.
The first two will basically be defaults where there is no user setting (eg for a new user).
I considered implementing a set of functions, which I could then implement for the different systems (likely to be through ini files), but is this the best way?
(c++)
namespace config
{
void Init(const std::string &AppName);
//updates config for keys/sections that don't exist (ie don't overwrite changes by advanced users by rewriting the entire file)
void Defaults (std::map<std::string,std::map<std::string,std::string> > &Map);
void SystemDefaults (std::map<std::string,std::map<std::string,std::string> > &Map);
void Set (const std::string &Section, const std::string &Key, const std::string &Value);
void SetSystem (const std::string &Section, const std::string &Key, const std::string &Value);
void SetUser (const std::string &Section, const std::string &Key, const std::string &Value);
void SetUserSystem (const std::string &Section, const std::string &Key, const std::string &Value);
std::string GetValue (const std::string &Section, const std::string &Key);
}
I know windows has a set of directories for such settings, but are these the correct dirs for my needs?
EDIT: I would rather go with files (ini or xml), rather than using say the windows registery. However wheres the best places to put these config files under each OS?
Under Vista I found these, which seem to fit my groups, however what of older windows versions (I need to support win2000, XP, etc), and does mac/linux have there own simelar folders?
Global settings - <SYSDRIVE>\Users\Default\Appdata\Roaming
Global system settings - <SYSDRIVE>\Users\Default\Appdata\Local
User settings - <SYSDRIVE>\Users\<USER>\AppData\Roaming
User system settings - <SYSDRIVE>\Users\<USER>\AppData\Local
If you are a boost user, you might take a look at the program options library, it supports using config files as well as environment variables and (of course) command line options.
It is designed to be portable, so that should ease your cross-platform headaches.
See also Where should cross-platform apps keep their data?
There are (at least) three reasonable choices:
Registry: This is my least favorite because of portability and relative opacity.
Environment variables: I recommend using one (just one) that points to a place where your material is kept - an "installation directory" or some such.
Files: Both a/the user-home directory (or in a subdirectory thereof) and project/product directory are suitable for storing things.
You might want to use a simple keyword=value paradigm, and basic rules so your variables - settings - can be read by more than one type of code very easily. For example, I typically use the Java paradigm for Property files and use matching behavior C code so both my codelines can easily read the settings.