• Qt5 Signal Slot Syntax Python
• Qt5 Signal Slot Syntax Example
• Qt5 Signal Slot Syntax Tool
• Qt5 Signal Slot Syntax Analyzer

The connection type is determined when the signal is emitted. Qt::DirectConnection: This slot is invoked immediately when the signal is emitted. The slot is executed in the signaling thread. Qt::QueuedConnection: The slot is invoked when control returns to the event loop of the receiver’s thread. The slot is executed in the receiver’s thread. Signals and slots are loosely coupled: A class which emits a signal neither knows nor cares which slots receive the signal. Qt's signals and slots mechanism ensures that if you connect a signal to a slot, the slot will be called with the signal's parameters at the right time. Signals and slots can take any number of arguments of any type. New Syntax in Qt5. The new syntax looks like this: QObject::connect(& a, & Counter::valueChanged, & b, & Counter:: setValue); Why the new syntax? I already explained the advantages of the new syntax in a dedicated blog entry. To summarize, the new syntax allows compile-time checking of the signals and slots. Signal-Slot is one of the fundamental topics of Qt one should have a firm grasp to write Qt applications. I have been developing Qt C application on Windows/Linux platforms about 3 and a half. In this video iam going to show you how you can create Signal And Slots in Qt5 C with Practical Examples, in this we are going to introduce Signal And Slot.

How can I pass signal or slot (member-function, new syntax in Qt 5) as a parameter to function and then call connect?

e.g. I want to write a function that waits for a signal.

Note: It is not compile - PointerToMemberFunction is my question.

Is there any way to pass list of signals to this function for connection?

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...

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...

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...

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...

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...

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))...

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...

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(); ...

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&...

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...

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...

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...

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...

.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:...

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...

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...

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...

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>. ...

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.

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...

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...

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...

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...

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...

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:...

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...

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...

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

Qt5 Signal Slot Syntax Python

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...

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...

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...

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...

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...

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....

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,...

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...

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); ...

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...

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 =...

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)...

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...

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....

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...

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:...

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:...

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'; } ...

Why are shaders and programs stored as integers in OpenGL?

Qt5 Signal Slot Syntax Example

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...

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>...

Introduction

Remarks

Official documentation on this topic can be found here.

A Small Example

Signals and slots are used for communication between objects. The signals and slots mechanism is a central feature of Qt and probably the part that differs most from the features provided by other frameworks.

The minimal example requires a class with one signal, one slot and one connection:

counter.h

The main sets a new value. We can check how the slot is called, printing the value.

Finally, our project file:

The new Qt5 connection syntax

The conventional connect syntax that uses SIGNAL and SLOT macros works entirely at runtime, which has two drawbacks: it has some runtime overhead (resulting also in binary size overhead), and there's no compile-time correctness checking. The new syntax addresses both issues. Before checking the syntax in an example, we'd better know what happens in particular.

Let's say we are building a house and we want to connect the cables. This is exactly what connect function does. Signals and slots are the ones needing this connection. The point is if you do one connection, you need to be careful about the further overlaping connections. Whenever you connect a signal to a slot, you are trying to tell the compiler that whenever the signal was emitted, simply invoke the slot function. This is what exactly happens.

Here's a sample main.cpp:

Hint: the old syntax (SIGNAL/SLOT macros) requires that the Qt metacompiler (MOC) is run for any class that has either slots or signals. From the coding standpoint that means that such classes need to have the Q_OBJECT macro (which indicates the necessity to run MOC on this class).

The new syntax, on the other hand, still requires MOC for signals to work, but not for slots. If a class only has slots and no signals, it need not have the Q_OBJECT macro and hence may not invoke the MOC, which not only reduces the final binary size but also reduces compilation time (no MOC call and no subsequent compiler call for the generated *_moc.cpp file).

Connecting overloaded signals/slots

While being better in many regards, the new connection syntax in Qt5 has one big weakness: Connecting overloaded signals and slots. In order to let the compiler resolve the overloads we need to use static_casts to member function pointers, or (starting in Qt 5.7) qOverload and friends:

Multi window signal slot connection

Qt5 Signal Slot Syntax Tool

A simple multiwindow example using signals and slots.

There is a MainWindow class that controls the Main Window view. A second window controlled by Website class.

The two classes are connected so that when you click a button on the Website window something happens in the MainWindow (a text label is changed).

I made a simple example that is also on GitHub:

mainwindow.h

mainwindow.cpp

website.h

website.cpp

Project composition:

Consider the Uis to be composed:

• Main Window: a label called 'text' and a button called 'openButton'
• Website Window: a button called 'changeButton'

Qt5 Signal Slot Syntax Analyzer

So the keypoints are the connections between signals and slots and the management of windows pointers or references.