Recent questions tagged C++

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c++ - Does C++11 allow dollar signs in identifiers?

Are dollar-signs allowed in identifiers in C++03? covers that dollar signs in identifiers are not allowed in C+ ... used as an identifier name? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Apply function to all Eigen matrix element

I have an Eigen::MatrixXd and I would like to modify all its elements by applying a function component-wise. ... way to achieve this result? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Returning a void?

I do not understand why this code compiles without error: #include <iostream> template <class T> struct Test { ... is it a compiler tolerance? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - QDialog exec() and getting result value

I have subclassed QDialog to implement functionality similar to QMessageBox ( I needed this to allow for ... the complete version. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Are Variadic macros nonstandard?

For debugbuilds, I usually use Clang, as it formats warnings and errors better, and makes it a ... Preprocessor is interpreted independently)? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why do reference type members cause implicitly-declared copy assignment operator to be deleted

From CPP Reference: Deleted implicitly-declared copy assignment operator The implicitly-declared or defaulted copy assignment ... C# and Java). See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - ifstream not reading EOF character

I am creating a program (In C++) that takes an ASCII file and reads a few values from each line until it ... that causes it to return that? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - BOOST ASIO - How to write console server

I have to write asynchronous TCP Sever. TCP Server have to be managed by console (for eg: remove client, show ... : showClients(); break } } See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How to show QSqlQueryModel in QML?

I want to show QSqlQueryModel in qml TableView but I don't Wan't to create separate QML file for each new ... user may enter any SQL Query. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - C++11 std::mutex in Visual Studio 2012 deadlock when locked from DllMain()

I am seeing a deadlock with std::mutex when the mutex is locked from DllMain() ... : PRIMARY_PROBLEM_CLASS: APPLICATION_HANG_HungIn_LoaderLock See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Inverse fourier transformation in OpenCV

I am new in OpenCV and image processing algorithms. I need to do inverse discrete fourier transformation in OpenCV in C+ ... dst = planes[0]; } See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Removing '#include <algorithm>' doesn't break the code

Maybe this is a very silly question, but the book I'm reading instructed me to write a piece of code that uses ... system("pause"); return 0; } See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How to safely destruct a QThread?

I want to properly destruct a QThread in Qt 5.3. So far I have got: MyClass::MyClass(QObject *parent ... Destroyed while thread is still running See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Initializing a ublas vector from a C array

I am writing a Matlab extension using the C++ ublas library, and I would like to be able to initialize my ublas vectors ... v[0]=0 pv[0]=0 See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How can I implement a map with different data types as values?

I want to put two (not more) different data types as values into a map as shown in the following example: ... to only two different data types. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Unable to read frames from VideoCapture from secondary webcam with OpenCV

Code: Simple example that works perfectly with primary webcam (device 0): VideoCapture cap(0); if (!cap. ... Any help will be appreciated. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - variable nested for loops

I'm trying to figure out how I can use recursion to do n-level nested for loops. For example, if n=3, there would be 3 ... 1 3 2 4 3 . . . 12 1 See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why doesn't left bit shift << shift beyond 31 for long int datatype?

I want to use the following code in my program but gcc won't allow me to left shift my 1 beyond 31. ... maximum value the datatype can hold. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How do you set the cout locale to insert commas as thousands separators?

Given the following code: cout << 1000; I would like the following output: 1,000 This can be done using std::locale, ... '))); cout << 1000; } See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How can I create a std::set of structures?

I need to create a stl::set of structures. Therefore, I wrote the following: stl::set <Point> mySet; // Point ... How do I get my code compiled? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Efficient Multiply/Divide of two 128-bit Integers on x86 (no 64-bit)

Compiler: MinGW/GCC Issues: No GPL/LGPL code allowed (GMP or any bignum library for that matter, is overkill for ... ) just how it will work. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Can a single member of a class template be partially specialized?

I came across an interesting point that I wasn't able to explain or find an explanation for. Consider the ... foresee? Is it an oversight? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why can I call base template class method from derived class

I decided to test one of the examples in "Effective C++" and I'm not getting the result I expected. So, ... Is the above code correct or not? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - when do we need to pass the size of array as a parameter

I am a little bit confused about pass an array in C/C++. I saw some cases in which the signature is like this ... and when and how to use it? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How is its lifetime of a return value extended to the scope of the calling function when it is bound to a const reference in the calling function?

"If you return a value (not a reference) from the function, then bind it to a const reference in the ... Am I missing something trivial here? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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362 views

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c++ - multiple inheritance: unexpected result after cast from void * to 2nd base class

My program needs to make use of void* in order to transport data or objects in dynamic invocation situation, so that ... be a bug in gcc? Thanks See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why does the compiler choose bool over string for implicit typecast of L""?

Having recently introduced an overload of a method the application started to fail. Finally tracking it down, the ... make an incorrect guess. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Does reinterpret_cast lead to undefined behavior?

I have a class template A which contains a container of pointers (T*): template <typename T> class A { ... use such conversions in real life? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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