Recent questions tagged C++

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I would like to compile this. program.c #include <libavcodec/avcodec.h> int main(){ int i = avpicture_get_size ... . Why is this happening? 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++ - Blur effect over a QWidget in Qt

Is there any way to blur a widget in Qt? For instance, supose I want to create a 'Loading...' dialog ... the background (not active window). 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 is std::unordered_map slow, and can I use it more effectively to alleviate that?

I've recently found out an odd thing. It seems that calculating Collatz sequence lengths with no caching at all ... Outputs Time taken: 0.324586 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++ - pthreads: thread starvation caused by quick re-locking

I have a two threads, one which works in a tight loop, and the other which occasionally needs to ... of handling this synchronization process? 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++ - Concat two `const char` string literals

Is it possible to concat two string literals using a constexpr? Or put differently, can one eliminate macros in ... those type of macros. 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++ - What lasts after using std::move c++11

After using std::move in a variable that might be a field in a class like: class A { public: vector<string> ... in myVector after the std::move? 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++ - Implicit conversion from char** to const char**

Why my compiler(GCC) doesnt implicitly cast from char** to const char**? Thie following code: #include <iostream> ... char**)' [-fpermissive] 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++ - std::vector iterator invalidation

There have been a few questions regarding this issue before; my understanding is that calling std::vector::erase will ... me that it's valid. 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++ - Is the size of a struct required to be an exact multiple of the alignment of that struct?

Once again, I'm questioning a longstanding belief. Until today, I believed that the alignment of the following struct ... focus is on C++. 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++ - operator< comparing multiple fields

I have the following operator< that is supposed to sort first by a value, then by another value: inline bool ... also longer than the first one 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 async_* functions and shared_ptr's

I frequently see this pattern in code, binding shared_from_this as the first parameter to a member function and ... the member function returns. 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++ - Inheritance and method overloading

Why C++ compiler gives this error? Why i can access lol() from B, but can not access rofl() [without ... not take 0 arguments 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++ - Is it possible to determine if a type is a scoped enumeration type?

Is there a type trait, or is it possible to write a type trait is_scoped_enum<T> such that: if T is a ... , is_scoped_enum<T>::value is false 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++ - Rationale of enforcing some operators to be members

There are 4 operators in C++ which can be overloaded but cannot be overloaded as freestanding (aka nonmember, ... ideas about the other three? 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++ - Override a member function with different return type

Consider the example below: #include <iostream> using namespace std; class base { public: virtual int func() ... . Is my understanding correct? See Question&Answers more detail:os...

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

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315 views

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c++ - Same random numbers every time I run the program

My random numbers that output, output in the same sequence every time I run my game. Why is this happening? I have ... = 1 + rand() % 6; See Question&Answers more detail:os...

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

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251 views

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c++ - Logical AND, OR: Is left-to-right evaluation guaranteed?

Is left-to-right evaluation of logical operators (&& ||) guaranteed? Let's say I have this: SDL_Event event; if ( ... ) than if (b && a). See Question&Answers more detail:os...

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

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440 views

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c++ - Get HWND on windows with Qt5 (from WId)

I am trying to convert a Qt4 Application to Qt5. The only thing I couldn't figure out is how to get the HWND ... or some other way to get this. See Question&Answers more detail:os...

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

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220 views

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c++ - Why does same_as concept check type equality twice?

Looking at the possible implementation of the same_as concept at https://en.cppreference.com/w/cpp/concepts/same_as i ... ? Isn't it redundant? 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++ - writing directly to std::string internal buffers

I was looking for a way to stuff some data into a string across a DLL boundary. Because we use different ... dllGaveUs( &vectorToFillIn[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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509 views

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c++ - how can I fully disable resizing a window including the resize icon when the mouse hovers the border?

I used: setFixedSize(size()); to stop the window from resizing, but the resize arrows still appear when the ... arrows when crossing the border? See Question&Answers more detail:os...

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

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277 views

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c++ - Keyboard Input & the Win32 message loop

How do I handle key presses and key up events in the windows message loop? I need to be able to call two functions ... , whereas I'm using C++. See Question&Answers more detail:os...

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

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386 views

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c++ - Placement new and assignment of class with const member

Why is that undefined behaviour? struct s { const int id; // <-- const member s(int id): id(id) {} ... ). This question arose from this answer. See Question&Answers more detail:os...

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

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554 views

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c++ - Can someone please explain the "indices trick"?

I noticed the "indices trick" being mentioned in the context of pretty-printing tuples. It sounded interesting, ... packs and variadic tuples? 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++ - Determine Process Info Programmatically in Darwin/OSX

I have a class with the following member functions: /// caller pid virtual pid_t Pid() const = 0; /// physical memory ... 4.0 No obj-c OSX 10.5 See Question&Answers more detail:os...

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

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152 views

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c++ - Bjarne Stroustrup says we must avoid linked lists

I saw this video on YouTube: https://www.youtube.com/watch?v=YQs6IC-vgmo in which Bjarne says it is ... suggest any sources to learn vectors? See Question&Answers more detail:os...

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

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189 views

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c++ - avoiding the tedium of optional parameters

If I have a constructor with say 2 required parameters and 4 optional parameters, how can I avoid writing 16 ... (And easier to maintain?) See Question&Answers more detail:os...

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

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405 views

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c++ - Check if a pointer points to allocated memory on the heap

I want to know if a pointer points to a piece of memory allocated with malloc/new. I realize that the ... looking for performance is motivated. See Question&Answers more detail:os...

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

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