Qt Signal And Slots Callback
In Qt, we have an alternative to the callback technique: We use signals and slots. A signal is emitted when a particular event occurs. Qt's widgets have many predefined signals, but we can always subclass widgets to add our own signals to them. The callbacks can be signals and slots (via QtCallback) or arbitrary functions using tr1::function, std::function, boost::function or a similar wrapper. Qt 5 provides support for connecting signals to arbitrary functions out of the box and to lambdas when using C11. The Qt Signal Slot Vs Callback Roulette Double Up. So this strategy can be quite Qt Signal Slot Vs Callback rewarding, but at the same time risky. Whenever you claim a casino bonus, the first thing you should Qt Signal Slot Vs Callback do is to take the whole amount and bet on either RED or BLACK on Roulette. The connection mechanism uses a vector indexed by signals. But all the slots waste space in the vector and there are usually more slots than signals in an object. So from Qt 4.6, a new internal signal index which only includes the signal index is used. While developing with Qt, you only need to know about the absolute method index. New games Qt Signal Slot Callback are constantly being released at JackpotCity Online Casino, and table games Qt Signal Slot Callback are no different. While standard blackjack, roulette and other table games Qt Signal Slot Callback are available, new versions are constantly Qt Signal Slot Callback released, or original games refreshed, to keep the line-up exciting.
I have a MainWindow that contains a custom widget with a QTextEdit in it. I would like to create a signal/slot between the MainWindow and the QTextEdit.
In MainWindow I have:
But this does not work. Is it even possible to create such signal/slot combination?
why bother - let Qt do all the magic :) Just name your slot (in the mainWindow) like that:
And you're done. More info here: http://doc.qt.io/qt-5/qmetaobject.html#connectSlotsByName important: 'object name' part means name of the object - not variable name. If you design your window in QtDesigner it should be set (in ui.setupUi method). if not - set it manually (by calling setObjectName
Just watch out for number of arguments in your slot. Here's what I do: I simply copy the signal prototype (from from header or the doc - eg: http://doc.qt.io/qt-5/qabstractitemmodel.html#dataChanged - watch out again for the weird whitespace between '::' and method name [some kind of an unbreakable-zerowidth-space] - only present when copying from v5.x doc), and prepend it with on_objectName_. That guarantees, that your slot will be ok to connect it to the signal
Translating a character array into a integer string in C++
c++,arrays,string
If you want a sequence of int, then use a vector<int>. Using the key_char string, the values of the chars in it will serve as the initial value of the ints. std::vector<int> key_num(key_char.begin(), key_char.end()); Then, iterate over each character of key_num and convert it to the equivalent int value for...
Why are shaders and programs stored as integers in OpenGL?
c++,opengl,opengl-es,integer,shader
These integers are handles.This is a common idiom used by many APIs, used to hide resource access through an opaque level of indirection. OpenGL is effectively preventing you from accessing what lies behind the handle without using the API calls. From Wikipedia: In computer programming, a handle is an abstract...
undefined reference to `vtable for implementation' error
c++,build,makefile
I think you just misspelled CFLAGS in CFLAGES=-c -Wall I'm guessing this is the case since g++ ../src/main.cpp -I ../include/ does not have the -c option...
Can python script know the return value of C++ main function in the Android enviroment
python,c++
For your android problem you can use fb-adb which 'propagates program exit status instead of always exiting with status 0' (preferred), or use this workaround (hackish... not recommended for production use): def run_exe_return_code(run_cmd): process=subprocess.Popen(run_cmd + '; echo $?',stdout=subprocess.PIPE,shell=True) (output,err)=process.communicate() exit_code = process.wait() print output print err print exit_code return exit_code...
Passing something as this argument discards qualifiers
c++,c++11
There are no operator[] of std::map which is const, you have to use at or find: template<> struct Record::getDispatcher<std::string> { static std::string impl(Record const& rec, std::string& const field) { return rec.fieldValues_.at(field); // throw if field is not in map. } }; or template<> struct Record::getDispatcher<std::string> { static std::string impl(Record const&...
dispatch response packet according to packet sequence id
c++,boost,boost-asio
You could use std::promise and std::future (or their boost counterparts if your are not yet on C++11). The idea is to store a std::shared_ptr<std::promise<bool>> with the current sequence id as a key in the map whenever a request is sent. In the blocking send function you wait for the corresponding...
Rotating a Label In Qt with Python
python,qt
Not 100% sure what you're trying to achieve, but rotating the image / pixmap and leaving the label's paintEvent unchanged seems easier: # load your image image = QtGui.QPixmap(_fromUtf8(':/icons/BOOM_OUT.png')) # prepare transform t = QtGui.QTransform() t.rotate(45) # rotate the pixmap rotated_pixmap = pixmap.transformed(t) # and let the label show the...
C++11 Allocation Requirement on Strings
c++,string,c++11,memory,standards
Section 21.4.1.5 of the 2011 standard states: The char-like objects in a basic_string object shall be stored contiguously. That is, for any basic_string object s, the identity &*(s.begin() + n) &*s.begin() + n shall hold for all values of n such that 0 <= n < s.size(). The two...
3 X 3 magic square recursively
c++,algorithm,math,recursion
Basically, you are finding all permutations of the array using a recursive permutation algorithm. There are 4 things you need to change: First, start your loop from pos, not 0 Second, swap elements back after recursing (backtracking) Third, only test once you have generated each complete permutation (when pos =...
Same function with and without template
c++,c++11
The main reason to do something like this is to specialize void integerA(int x) to do something else. That is, if the programmer provides as input argument an int to member function abc::integerA then because of the C++ rules instead of instantiating the template member function the compiler would pick...
MFC visual c++ LNK2019 link error
c++,mfc
The header file provides enough information to let you declare variables. And for that matter to just compile (but not link) code. When you link, the linker has to resolve e.g. function references such as a reference to ServerConnection::getLicenceRefused, by bringing in the relevant machine code. You have to tell...
Test if string represents “yyyy-mm-dd”
c++,command-line-arguments
If you can use boost library you could simple do it like this: string date('2015-11-12'); string format('%Y-%m-%d'); date parsedDate = parser.parse_date(date, format, svp); You can read more about this here. If you want a pure C++ solution you can try using struct tm tm; std::string s('2015-11-123'); if (strptime(s.c_str(), '%Y-%m-%d', &tm))...
Passing iterator's element to a function: wrong type of pointer
c++,pointers,stl,iterator
Preferred option: change isPrime to take a long (and pass *it to it). Secondary option: pass &*it instead of it. Your original code doesn't work because it is an iterator (which is a class) whereas the function expected long int * and there is no implicit conversion from iterator to...
C++ Isn't this a useless inline declaration?
c++,inline,private,member,protected
The Compiler can Access everything. The restrictions are only valid for the programmer. This means there are no restrictions for the Compiler to Access any variables! At the end every variable is just translated to an address which can be accessed. So for the Compiler it is no Problem to...
Validate case pattern (isupper/islower) on user input string
c++,user-input
The simplest thing you can do is to use a for/while loop. A loop will basically repeat the same instruction for a number of n steps or until a certain condition is matched. The solution provided is pretty dummy, if you want to read the first name and last name...
C++ template template
c++,templates
Your issue is that std::deque (and other standard containers) doesn't just take a single template argument. As well as the stored type, you can specify an allocator functor type to use. If you don't care about these additional arguments, you can just take a variadic template template and be on...
Type function that returns a tuple of chosen types
c++,templates,c++11,metaprogramming
You can do this without recursion by simply expanding the parameter pack directly into a std::tuple: template<My_enum... Enums> struct Tuple { using type = std::tuple<typename Bind_type<Enums>::type...>; }; To answer your question more directly, you can declare a variadic primary template, then write two specializations: for when there are at least...
how to sort this vector including pairs
c++,vector
You forgot the return statement in the function bool func(const pair<int,pair<int,int> >&i , const pair<int,pair<int,int> >&j ) { i.second.first < j.second.first ; } Write instead bool func(const pair<int,pair<int,int> >&i , const pair<int,pair<int,int> >&j ) { return i.second.first < j.second.first ; } Also you should include header <utility> where class std::pair...
No match for 'operator*' error
c++,c++11
As @101010 hints at: pay is a string, while hours_day is a float, and while some languages allow you to multiply strings with integers, c++11 (or any other flavor of c) doesn't, much less allow strings and floats to be multiplied together.
Marshal struct in struct from c# to c++
c#,c++,marshalling
Change this: [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 36)] private string iu; to this: [MarshalAs(UnmanagedType.LPStr)] private string iu; Note that this code is good only to pass a string in the C#->C++ direction. For the opposite direction (C++->C#) it is more complex, because C# can't easily deallocate C++ allocated memory. Other important thing:...
template template class specialization
c++,templates,template-specialization
The specialization still needs to be a template template argument. You passed in a full type. You want: template <class Type, class Engine> class random_gen<std::uniform_real_distribution, Type, Engine> { ... }; Just std::uniform_real_distribution, not std::uniform_distribution<Type>. ...
Implicit use of initializer_list
c++,c++11,initializer-list
Your program is not ill-formed because <vector> is guaranteed to include <initializer_list> (the same is true for all standard library containers) §23.3.1 [sequences.general] Header <vector> synopsis #include <initializer_list> ... Searching the standard for #include <initializer_list> reveals the header is included along with the following headers <utility> <string> <array> <deque> <forward_list>...
How can I convert an int to a string in C++11 without using to_string or stoi?
c++,string,c++11,gcc
Its not the fastest method but you can do this: #include <string> #include <sstream> #include <iostream> template<typename ValueType> std::string stringulate(ValueType v) { std::ostringstream oss; oss << v; return oss.str(); } int main() { std::cout << ('string value: ' + stringulate(5.98)) << 'n'; } ...
opencv window not refreshing at mouse callback
c++,opencv
your code works for me. But you used cv::waitKey(0) which means that the program waits there until you press a keyboard key. So try pressing a key after drawing, or use cv::waitKey(30) instead. If this doesnt help you, please add some std::cout in your callback function to verify it is...
Explicit instantiation of class template not instantiating constructor
c++,templates,constructor,explicit-instantiation
When the constructor is a template member function, they are not instantiated unless explicitly used. You would see the code for the constructor if you make it a non-template member function. template<typename T> class test { public: /*** template<typename T> test(T param) { parameter = param; }; ***/ test(T param)...
segfault accessing qlist element through an iterator
c++,iterator,qlist
(Edited away first 'answer', this is an actual attempt at an answer) My guess: QList<Msg> messages() const { return _messages; } It's returning a copy of the QList _messages, rather than a reference to it. I'm not sure that it would give the results you're seeing, but it looks wrong...
Incorrect Polar - Cartesian Coordinate Conversions. What does -0 Mean?
c++,polar-coordinates,cartesian-coordinates
You are converting to cartesian the points which are in cartesian already. What you want is: std::cout << 'Cartesian Coordinates:' << std::endl; std::cout << to_cartesian(to_polar(a)) << std::endl; std::cout << to_cartesian(to_polar(b)) << std::endl; //... Edit: using atan2 solves the NaN problem, (0, 0) is converted to (0, 0) which is fine....
Add more features to stack container
c++,visual-c++,stl
If this is interview question or something , and you have to do it anyways , you can do this like ,below code . derive from std::stack , and overload [] operator #include <iostream> #include <algorithm> #include <stack> #include <exception> #include <stdexcept> template <typename T> class myStack:public std::stack<T> { public:...
create vector of objects on the stack ? (c++)
c++,vector,heap-memory
Yes, those objects still exist and you must delete them. Alternatively you could use std::vector<std::unique_ptr<myObject>> instead, so that your objects are deleted automatically. Or you could just not use dynamic allocation as it is more expensive and error-prone. Also note that you are misusing reserve. You either want to use...
How to avoid user to click outside popup Dialog window using Qt and Python?
qt,user-interface,python-3.x,dialog,qt-creator
use setModal() like so; dialog.setModal(1); Or; dialog.setModal(true); ...
ctypes error AttributeError symbol not found, OS X 10.7.5
python,c++,ctypes
Your first problem is C++ name mangling. If you run nm on your .so file you will get something like this: nm test.so 0000000000000f40 T __Z3funv U _printf U dyld_stub_binder If you mark it as C style when compiled with C++: #ifdef __cplusplus extern 'C' char fun() #else char fun(void)...
Confused about returns in stack template
c++,templates,generic-programming
This depends on what you want the behaviour (protocol) of your class to be. Since you're logging into the error stream there, I assume you consider this an error condition to call pop() on an empty stack. The standard C++ way of signalling errors is to throw an exception. Something...
OpenCV - Detection of moving object C++
c++,opencv
Plenty of solutions are possible. A geometric approach would detect that the one moving blob is too big to be a single passenger car. Still, this may indicate a car with a caravan. That leads us to another question: if you have two blobs moving close together, how do you...
std::condition_variable – notify once but wait thread wakened twice
c++,multithreading
Converting comments into answer: condition_variable::wait(lock, pred) is equivalent to while(!pred()) wait(lock);. If pred() returns true then no wait actually takes place and the call returns immediately. Your first wake is from the notify_one() call; the second 'wake' is because the second wait() call happens to execute after the Stop() call,...
Issue when use two type-cast operators in template class
What you're trying to do makes little sense. We have subclass<int>. It is convertible to int&, but also to a lot of other reference types. char&. bool&. double&. The ambiguity arises from the fact that all the various overloads for operator<< that take any non-template argument are viable overload candidates...
How can I access the members of a subclass from a superclass with a different constructor?
c++,inheritance,constructor,subclass,superclass
This map: typedef map<string, Object> obj_map; only stores Object objects. When you try to put an Image in, it is sliced down and you lose everything in the Image that was not actually part of Object. The behaviour that you seem to be looking for is called polymorphism. To activate...
Method returning std::vector< />
Your error is actually coming from: array.push_back(day); This tries to put a copy of day in the vector, which is not permitted since it is unique. Instead you could write array.push_back( std::move(day) ); however the following would be better, replacing auto day...: array.emplace_back(); ...
.cpp:23: error: cannot convert ‘std::string’ to ‘const char*’ for argument ‘1’ to ‘int atoi(const char*)’
c++,string
Use stoi, it's the modern C++ version of C's atoi. Update: Since the original answer text above the question was amended with the following error message: ‘stoi’ was not declared in this scope Assuming this error was produced by g++ (which uses that wording), this can have two different causes:...
Parameters to use in a referenced function c++
c++,pointers,reference
Your code makes no sense, why are you passing someStruct twice? For the reference part, you should have something like: void names(someStruct &s) { // <<<< Pass struct once as a reference cout << 'First Name: ' << 'n'; cin >> s.firstname; cout << 'Last Name: ' << 'n'; cin...
Make a triangle shape in C++
This code works fine for a right angled triangle - * ** *** But I guess you want a triangle like this - * *** ***** Try this - #include <iostream> using namespace std; int main() { int i, j, k, n; cout << 'Please enter number of rows you...
Get an ordered list of files in a folder
c++,boost,boost-filesystem
The fanciest way I've seen to perform what you want is straight from the boost filesystem tutorial. In this particular example, the author appends the filename/directory to the vector and then utilizes a std::sort to ensure the data is in alphabetical order. Your code can easily be updated to use...
Strings vs binary for storing variables inside the file format
c++,file,hdf5,dataformat
Speaking as someone who's had to do exactly what you're talking about a number of time, rr got it basically right, but I would change the emphasis a little. For file versioning, text is basically the winner. Since you're using an hdf5 library, I assume both serializing and parsing are...
How can I tell clang-format to follow this convention?
c++,clang-format
Removing BreakBeforeBraces: Allman Seems to do what you want (for me). I'm using SVN clang though. Although you probably wanted it there for a reason. According to the clang-format docs, the AllowShortBlocksOnASingleLine should do exactly what you want (regardless of brace style). This might be a bug in clang-format....
Undefined behaviour or may be something with memset
c++,undefined-behavior
The A[32] in the method is actually just a pointer to A. Therefore, sizeof is the size of *int. Take the following test code: void szof(int A[32]) { std::cout << 'From method: ' << sizeof(A) << 'n'; } int main(int argc, char *argv[]) { int B[32]; std::cout << 'From main:...
Checking value of deleted object
It is very bad, accessing deleted objects as if they were not deleted will in the general case crash. There is no guarantee that the memory is still mapped inside the process and it could result in a virtual memory page fault. It is also likely that the memory will...
pointer to pointer dynamic array in C++
c++,arrays,pointers
The valid range of indices of an array with N elements is [0, N-1]. Thus instead of for example this loop for (int i=1; i <= n; i++) ^^^^ ^^^^^^ you have to write for ( int i = 0; i < n; i++ ) As you used operator new...
C++ & Qt: Random string from an array area
c++,arrays,string,qt,random
You should use the random header. #include <random> std::default_random_engine generator; std::uniform_int_distribution dist(0, 5); int StringIndex = dist(generator); std::string ChosenString = characters[StringIndex]; The above will generate a random index into your array. If you want to limit the range, change the constructor of dist, for example (dist(0,2) would only allow for...
Copy text and placeholders, variables to the clipboard
c++,qt,clipboard
You're not using the function setText correctly. The canonical prototype is text(QString & subtype, Mode mode = Clipboard) const from the documentation. What you want to do is assemble your QString ahead of time and then use that to populate the clipboard. QString message = QString('Just a test text. And...
In this chapter we will add some functionality to the window and we will learn how to obtain the values from the different widgets.
About Qt Signals and Slots
Qt (and therefore PySide/PyQt) has built-in signals and slots to control the most common functionalities of widgets. Signals are messages that are emitted by a widget when a certain event or action ocurs (a button was pressed, for example). Slots receive inputs from signals, and are able to perform common actions such as update a value or enable a widget. Signals and slots can be connected together as an easy way of achieving complex behaviors from common wiget interactions.
More info on signals and slot here at ZetCode.
Adding callbacks
The first action we want to be performed is to disable the cornerSpinBox when the cornerCheckBox is unchecked. To achieve this, we will define a callback function insde the class PCBOutlineCreator:
And we will connect the signal emitted when the state of the CheckBox changes to this callback:
Now, we can write the code to be executed inside the callback:
If we run the code, we can see that initially the cornersSpinBox is still enabled. As the initial state was unchecked, the state has not changed on reset and the signal was not sent. In order for the code to run as expected we have to either modify our UI file to make the checkbox enabled by default, modify the UI file to make the spinbox disabled by default, or perform either of these actions programatically using this sentence:
Using Qt Signals and Slots
Previously we added a callback function to disable the cornerSpinBox if it is unchecked. We can achieve the same result easily by connecting the corresponding signal and slot:
In this case, as stateChanged signal returns an int and setEnabled expects a bool, a lambda function was used to convert the value.
Extracting values from the widgets
In order to create the outline for our PCB, we need the dimensions specified by the user in the different widgets. For that pursose, we will add a callback to the save button that prints on the stdout the different values extracted from the widgets. first, we connect the signal to the callback:
And then we add the callback funtion. Inside this function, we request the values of the different widgets and we print them on the stdout:
When we run the code, and press the save button we get the following message on the stdout: