On my embedded system I don't have X11, Mac, Win, S60, etc. I keep getting a NULL ( 0 ) pointer returned from the create method of the QInputContextFactory class. I verified that QT_NO_LIBRARY is not defined.
On my Desktop Qt Build this works just fine.
I also verified that my custom key and parent are being passed to the method.
What could cause this to fail? -->
if (QInputContextFactoryInterface *factory =
qobject_cast<QInputContextFactoryInterface*>(loader()->instance(key))) {
result = factory->create(key);
}
Here is the entire method:
QInputContext *QInputContextFactory::create( const QString& key, QObject *parent )
{
QInputContext *result = 0;
#if defined(Q_WS_X11) && !defined(QT_NO_XIM)
if (key == QLatin1String("xim")) {
result = new QXIMInputContext;
}
#endif
#if defined(Q_WS_WIN)
if (key == QLatin1String("win")) {
result = new QWinInputContext;
}
#endif
#if defined(Q_WS_MAC)
if (key == QLatin1String("mac")) {
result = new QMacInputContext;
}
#endif
#if defined(Q_WS_S60)
if (key == QLatin1String("coefep")) {
result = new QCoeFepInputContext;
}
#endif
#ifdef QT_NO_LIBRARY
Q_UNUSED(key);
#else
qDebug() << "Here we are";
if (QInputContextFactoryInterface *factory =
qobject_cast<QInputContextFactoryInterface*>(loader()->instance(key))) {
result = factory->create(key);
}
#endif
if (result)
result->setParent(parent);
return result;
}
Within Qt, the QInputContextFactory class is front-end on loading input context plug-ins. It will fail to load an input context plug-in if it fails to exist, or hasn't been deployed properly. Input context plug-ins are typically stored under $QT_PLUGIN_PATH/inputmethods. As such, if there is no plug-in within that directory, the create method of the QInputContextFactory will return NULL.
Of note, Qt does provide a few mechanisms for customizing the location of plug-ins. Refer to the following for more detail on this:
http://qt-project.org/doc/qt-4.8/deployment-plugins.html
Related
I am writing code for a school project that will be used for a Chromebook charging station with security. The problem I am having now is when I am detecting if a Chromebook is actually in the slot after the user has been assigned one, I am using a rocker switch to simulate this but when I am declaring the pin to the rocker, the arduino verfier comes up with that
"'slot1' does not name a type".
Code is below:
//class
class Chromebook_slot {
public:
String Name = "";
String RFID_tag = "";
int rocker = 0;
boolean chromebook_in = false;
//class function to check if chromebook is in.
//if not, redirect already to reassigning so chromebook slot is entered as open and free.
void set_if_in()
{
int momen_1_state = digitalRead(momen_1);
int momen_2_state = digitalRead(momen_2);
// the button has been pushed down and the previous process has been completed
// eg. servos would have been reset if there was a previous user
if (momen_1_state == HIGH || momen_2_state == HIGH)
{
chromebook_in = digitalRead(this->rocker);
if (chromebook_in == 0)
{
re_assigning();
}
else
{
return;
}
}
}
};
//this is now outside the class..
//class declarations
Chromebook_slot slot1;
Chromebook_slot slot2;
//variables for rocker switches which will act for detecting chromebooks.
// in my final version, this will replaced by a photoresistor and laser.
slot1.rocker = 3;
slot2.rocker = 2;
Where the function re_assigning() is a separate function declared further in the code and just resets the slot as open for future use.
slot1.rocker = 3;
slot2.rocker = 2;
These are statements that cannot be at the top level of a C++ (or .ino) file. They need to be inside of a function. What's happening is the compiler is looking looking at the slot1 identifier through the lens of potential valid constructions. It sees an identifier, and about the only thing that could legally exist at this point in the code that starts with an identifier like that is some declaration, e.g. int a = 7;, or more abstractly some_type some_more_stuff. So it expects slot1 to be a type, which it isn't, hence the message.
If you want an assignment like those to happen early on in an Arduino program, the simplest thing you could do is put them in setup():
void setup() {
slot1.rocker = 3;
slot2.rocker = 2;
// ...
}
Or, you'd make these part of the Chromebook_slot's constructor, such that they could be given in slot1 and slot2's declaration:
class Chromebook_slot {
public:
Chromebook_slot(int rocker_init_value) {
rocker = rocker_init_value;
}
// ...
Or in a maybe less familiar but more proper form, using the constructor's initialization list:
class Chromebook_slot {
public:
Chromebook_slot(int rocker_init_value)
: rocker(rocker_init_value) {}
// ...
Once you have a constructor for Chromebook_slot, your variables can become:
Chromebook_slot slot1(3);
Chromebook_slot slot2(2);
I have an input QString that has HTML 4 entities, like õ that I’d like to decode. But I can’t find any facilities in Qt to do so. Is there a way to do so in Qt? If possible I’d like to avoid QTextDocument so I don’t have to bring in QtGui.
The HTML 4 entities are listed in this link:
https://www.w3schools.com/charsets/ref_html_entities_4.asp
Out of curiosity, I have looked a bit around.
I found this SO: How can i convert entity character(Escape character) to HTML in QT?. However, it uses QTextDocument (which is part of GUI) what OP wants to prevent.
The doc. of QTextDocument::setHtml() doesn't mention anything specific whether something is used which could be accessed directly (and is even part of the Qt core). Hence, I had a look into source code. I started with QTextDocument::setHtml() on woboq.org and followed the bread crumbs.
Finally, I ended up in qtbase/src/gui/text/qtexthtmlparser.cpp:
QString QTextHtmlParser::parseEntity()
{
const int recover = pos;
int entityLen = 0;
QStringRef entity;
while (pos < len) {
QChar c = txt.at(pos++);
if (c.isSpace() || pos - recover > 9) {
goto error;
}
if (c == QLatin1Char(';'))
break;
++entityLen;
}
if (entityLen) {
entity = QStringRef(&txt, recover, entityLen);
QChar resolved = resolveEntity(entity);
if (!resolved.isNull())
return QString(resolved);
if (entityLen > 1 && entity.at(0) == QLatin1Char('#')) {
entity = entity.mid(1); // removing leading #
int base = 10;
bool ok = false;
if (entity.at(0).toLower() == QLatin1Char('x')) { // hex entity?
entity = entity.mid(1);
base = 16;
}
uint uc = entity.toUInt(&ok, base);
if (ok) {
if (uc >= 0x80 && uc < 0x80 + (sizeof(windowsLatin1ExtendedCharacters)/sizeof(windowsLatin1ExtendedCharacters[0])))
uc = windowsLatin1ExtendedCharacters[uc - 0x80];
QString str;
if (QChar::requiresSurrogates(uc)) {
str += QChar(QChar::highSurrogate(uc));
str += QChar(QChar::lowSurrogate(uc));
} else {
str = QChar(uc);
}
return str;
}
}
}
error:
pos = recover;
return QLatin1String("&");
}
A table of named entities can be found in the same source file:
static const struct QTextHtmlEntity { const char name[9]; quint16 code; } entities[]= {
{ "AElig", 0x00c6 },
{ "AMP", 38 },
...
{ "zwj", 0x200d },
{ "zwnj", 0x200c }
};
Q_STATIC_ASSERT(MAX_ENTITY == sizeof entities / sizeof *entities);
These are bad news for OP:
The API of the QTextHtmlParser is private:
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
and it's part of Qt GUI.
If OP insists to prevent GUI dependencies, the only other chance I see is to duplicate the code (or just to re-implement it from scratch).
Using the twaindotnet library in C#, I'm wondering if there's a way to set the default datasource using the library.
As a feeble attempt, I've tried adding a SetDefault method to the DataSource class of twaindonet, like this
public static void SetDefault(Identity applicationId, IWindowsMessageHook messageHook, DataSource newDataSource)
{
var defaultSourceId = newDataSource.SourceId;
// Attempt to get information about the system default source
var result = Twain32Native.DsmIdentity(
applicationId,
IntPtr.Zero,
DataGroup.Control,
DataArgumentType.Identity,
Message.Set,
defaultSourceId);
if (result != TwainResult.Success)
{
var status = DataSourceManager.GetConditionCode(applicationId, null);
throw new TwainException("Error getting information about the default source: " + result, result, status);
}
}
which is called from the DataSourceManage class like this
public void SelectSource(DataSource dataSource)
{
DataSource.Dispose();
DataSource.SetDefault(ApplicationId, _messageHook, dataSource);
}
But when I try to use SetDefault, Twain32Native.DsmIdentity always results in Failure being returned.
I basically copied from SetDefault the setDefaultDataSource method from TWAIN sample Data Source and Application
pTW_IDENTITY TwainApp::setDefaultDataSource(unsigned int _index)
{
if(m_DSMState < 3)
{
cout << "You need to open the DSM first." << endl;
return NULL;
}
else if(m_DSMState > 3)
{
PrintCMDMessage("A source has already been opened, please close it first\n");
return NULL;
}
if(_index >= 0 && _index < m_DataSources.size())
{
m_pDataSource = &(m_DataSources[_index]);
// set the specific data source
TW_UINT16 twrc;
twrc = _DSM_Entry(
&m_MyInfo,
0,
DG_CONTROL,
DAT_IDENTITY,
MSG_SET,
(TW_MEMREF) m_pDataSource);
switch (twrc)
{
case TWRC_SUCCESS:
break;
case TWRC_FAILURE:
printError(0, "Failed to get the data source info!");
break;
}
}
else
{
return NULL;
}
return m_pDataSource;
}
Any help would be greatly appreciated.
The possible cause is that the version of your TWAIN DSM is too low. Only DSM 2.0 or above supports setting default TWAIN data source.
I have in an Object an QVector of Coordinates (my type) that I want to transfer to an other Vector ( I validate and than want to use ist ).
Header
bool getVector(QVector<Coordinates> &getCoordinates );
C File
static QVector<Coordinates> current;
int getVector( QVector<Coordinates> &getCoordinates)
{
.... stuff ...
getCoordinates = current;
.... stuff ....
return 0;
}
And I use it like
....
QVector<Coordinates> currentCoordinates;
getVector(currentCoordinates);
currentCoordinates.X // CRASH
The debugger goes to this line where an Live Crash happens
inline QVector(const QVector<T> &v) : d(v.d) { d->ref.ref(); if (!d->sharable) detach_helper(); }
So my how can I fix this? As I can use this to get all the other Variables with this methode.
A likely cause of your problem is that current has not been constructed before getVector is called. Initialization of static objects in C++ is a thorny area, and a frequent source of bugs - for more information, see this question, and the static initialization order fiasco FAQ entry.
A simple solution to this problem is to provide access to current via a function, i.e. replace
static QVector<Coordinates> current;
with
static QVector<Coordinates>& getCurrent()
{
static QVector<Coordinates> current;
return current;
}
Note, however, that the function as written above is not thread-safe. If multiple threads may call getCurrent, then it should be protected with a QMutex.
For gareth and the Forum :
the header:
typedef QVector<Coordinates> VesselCoordinates;
bool (*getVessel)(Charakter forCharakter, Vessel& getVessel,VesselCoordinates &getCoordinates );
later i bind tis function pointer to an static function ( cause this part of my Program will be one day convertet to c)
cpp file lower layer:
static struct {
Charakter currentPlayerVessel;
VesselCoordinates possibility;
}data;
static bool getVessel(Charakter forCharakter, Vessel& getVessel,VesselCoordinates &getCoordinates );
// funktion to bind the funktion pointer to this static funktion so it can be called outside the File
static bool serverNamespace::getVessel(Charakter forCharakter, Vessel& getVessel,VesselCoordinates &getCoordinates )
{
bool retValue= false;
if ( forCharakter == data.currentPlayerVessel){
// TODO abfragen ob die Adresse regestriert ist!
if ((true == minSize()) and ((true == shipsInRow())or (true == shipsInLine())))
{
retValue = true;
Vessel test = (Vessel)data.possibility.size();
getVessel = test;
getCoordinates = data.possibility;
}
}
return retValue;
}
And then i can use this in the upper layer cpp file to get the information i need:
// in an Funktion :
VesselCoordinates currentCoordinates;
currentCoordinates.clear();
Vessel currentVessel;
if (true == basicFleet->getVessel(currentCharakter,currentVessel, currentCoordinates ))
// doing stuff to it
so its worik fine but your idea worked just as fine. Maybe you can see why my idea is also working.
Thank you
elektor
I wrote a program to test my binary tree and when I run it, the program seems to crash (btree.exe has stopped working, Windows is checking for a solution ...).
When I ran it through my debugger and placed the breakpoint on the function I suspect is causing it, destroy_tree(), it seemed to run as expected and returned back to the main function. Main, in turn, returned from the program but then the cursor jumped back to destroy_tree() and looped recusively within itself.
The minimal code sample is below so it can be ran instantly. My compiler is MinGW and my debugger is gdb (I'm using Code::Blocks).
#include <iostream>
using namespace std;
struct node
{
int key_value;
node *left;
node *right;
};
class Btree
{
public:
Btree();
~Btree();
void insert(int key);
void destroy_tree();
private:
node *root;
void destroy_tree(node *leaf);
void insert(int key, node *leaf);
};
Btree::Btree()
{
root = NULL;
}
Btree::~Btree()
{
destroy_tree();
}
void Btree::destroy_tree()
{
destroy_tree(root);
cout<<"tree destroyed\n"<<endl;
}
void Btree::destroy_tree(node *leaf)
{
if(leaf!=NULL)
{
destroy_tree(leaf->left);
destroy_tree(leaf->right);
delete leaf;
}
}
void Btree::insert(int key, node *leaf)
{
if(key < leaf->key_value)
{
if(leaf->left!=NULL)
insert(key, leaf->left);
else
{
leaf->left = new node;
leaf->left->key_value = key;
leaf->left->left = NULL;
leaf->left->right = NULL;
}
}
else if (key >= leaf->key_value)
{
if(leaf->right!=NULL)
insert(key, leaf->right);
else
{
leaf->right = new node;
leaf->right->key_value = key;
leaf->right->left = NULL;
leaf->right->right = NULL;
}
}
}
void Btree::insert(int key)
{
if(root!=NULL)
{
insert(key, root);
}
else
{
root = new node;
root->key_value = key;
root->left = NULL;
root->right = NULL;
}
}
int main()
{
Btree tree;
int i;
tree.insert(1);
tree.destroy_tree();
return 0;
}
As an aside, I'm planning to switch from Code::Blocks built-in debugger to DDD for debugging these problems. I heard DDD can display visually pointers to objects instead of just displaying the pointer's address. Do you think making the switch will help with solving these types of problems (data structure and algorithm problems)?
Your destroy_tree() is called twice, you call it once and then it gets called after the execution leaves main() from the destructor.
You may think it should work anyway, because you check whether leaf!=NULL, but delete does not set the pointer to NULL. So your root is not NULL when destroy_tree() is called for the second time,
Not directly related (or maybe it is) to your problem, but it's good practice to give structs a constructor. For example:
struct node
{
int key_value;
node *left;
node *right;
node( int val ) : key_val( val ), left(NULL), right(NULL) {}
};
If you do this, your code becomes simpler, because you don't need worry about setting the pointers when you create a node, and it is not possible to forget to initialise them.
Regarding DDD, it;'s a fine debugger, but frankly the secret of debugging is to write correct code in the first place, so you don't have to do it. C++ gives you a lot of help in this direction (like the use of constructors), but you have to understand and use the facilities it provides.
Btree::destroy_tree doesn't set 'root' to 0 after successfully nuking the tree. As a result, the destructor class destroy_tree() again and you're trying to destroy already destroyed objects.
That'll be undefined behaviour then :).
Once you destroy the root.
Make sure it is NULL so it does not try to do it again (from the destructor)
void Btree::destroy_tree(node *leaf)
{
if(leaf!=NULL)
{
destroy_tree(leaf->left);
destroy_tree(leaf->right);
delete leaf;
leaf = NULL; // add this line
}
}