Recent questions tagged C++

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c++ - std::hash specialization using sfinae?

As an exercise I was trying to see if I could use SFINAE to create a std::hash specialization for std:: ... . Can someone help me understand? 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++ - Large (0,1) matrix multiplication using bitwise AND and popcount instead of actual int or float multiplies?

For multiplying large binary matrices (10Kx20K), what I usually to do is to convert the matrices to float ones and ... for a number of reasons. 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++ - Convert single char to int

How can I convert char a[0] into int b[0] where b is a empty dynamically allocated int array I have tried char ... 1 of int atoi(const char*)' 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++ - openCV: How to split a video into image sequence?

Using opencv, how can one split a video into an image sequence? How can i split it so that the output will be a sequence of images? 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 I need to acquire a lock to modify a shared "atomic" variable before notifying condition_variable

Accoding to cppreference.com: The thread that intends to modify the variable has to acquire a std::mutex ( ... o acquire the s_mtx lock? 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++ strtok skips second token or consecutive delimiter

I am trying to read CSV comma delimited file, content of file are one,,three And code to read file is this ... ); As well it does not works 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++ - Using only g++ works, but not "g++ -c" and ld

I have the following source code in main.cpp: #include <iostream> #include <iomanip> int main() { std ... undefined reference to `__cxa_atexit' 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 safe to remove const via const_cast and invoke a non-const function that does not modify the resulting object?

I know that casting away const-ness should be done with care, and any attempt to remove const-ness from an initially ... ; // is this safe? } 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++ - Access violation writing location 0xcccccccc

For the past 2 days I've been stuck on a violation which I can't seem to get to go away. I've ... other classes and it all stopped working! 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++ - Qt - QPushButton text formatting

I have a QPushButton and on that I have a text and and icon. I want to make the text on the button to be ... only way? Anyone has a better idea? 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++ - redirection of ./a.out is not capturing segmentation fault

I run the command ./a.out < in &> output.txt I want the errors also to be placed in output.txt. The exit ... and the file output.txt was empty. 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++ - cannot convert 'const char*' to 'LPCWSTR {aka const wchar_t*}'

I'm getting an error in my C++ code that I can't quite make sense of. The stripped down code bits are here ... How can I fix this issue? 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++ - opencv create mat from camera data

in my programm I have function that takes the image from camera and should pack all data in OpenCV Mat ... varible correctly? Thank you. 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 use something like `std::basic_istream<std::byte>`

This question aims for using std::byte with standard input-output. Are there any plans to add proper function ... kind of thing work already? 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++ - Visual Studio Compiler warning C4250 ('class1' : inherits 'class2::member' via dominance)

The following code generates warning C4250. My question is, what's the best solution to it? class A { virtual ... s everyone's view on 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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349 views

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c++ - Convert a QImage to grayscale

I have a QImage and I need to convert it to grayscale, then later paint over that with colors. I found an ... to convert a QImage to grayscale? See Question&Answers more detail:os...

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

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329 views

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c++ - Difference between Locks, Mutex and Critical Sections

There is an existing question regarding difference between Mutex and Critical section but it does not deal with ... and non-signalled states 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++ - Why overloaded new operator is implicitly static and no scope resolution required to construct the object

Why overloaded new operator is implicitly static and how we are able to allocate memory by calling overloaded new operator ... C; delete p; } 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++ - curl WRITEFUNCTION and classes

class Filter{ private: string contents; bool Server(void); public: void handle(void *, size_t, size_t, void *); } ... .. how can i rectify 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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c++ - Using a template alias instead of a template within a template

From a previous question: Doing a static_assert that a template type is another template Andy Prowl provided me with ... } Can this be solved? See Question&Answers more detail:os...

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

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233 views

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c++ - How to find out what dependencies (i.e other Boost libraries) a particular Boost library requires?

For any C++ Boost library, how can one find out which Boost library(ies) it requires ? Example (not ... Boost library "date_time". Regards, See Question&Answers more detail:os...

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

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190 views

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c++ - Is the unordered_map really unordered?

I am very confused by the name 'unordered_map'. The name suggests that the keys are not ordered at all. But ... is ordered by their hash value? See Question&Answers more detail:os...

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

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476 views

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c++ - CMake cannot find source file (add_executable)

I have been trying to follow the vendor's tutorial here: CMake-Tutorial, look over the documentation here: ... would be very much 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++ - Why does a quoted string match bool method signature before a std::string?

Given the following methods: // Method 1 void add(const std::string& header, bool replace); //Method 2 ... method signature being selected... 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++ - Error:"invalid comparator" when sorting using custom comparison function

I am trying to sort some integers and make odd integers followed by even ones. I am using Visual Studio 2015. Here ... error. How to modify 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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150 views

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c++ - std::tuple memory alignment

Is there any formal specification for the layout and memory alignment for the pseudo members of a tuple? Is ... memory have unknown alignment? See Question&Answers more detail:os...

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

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1.8k views

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c++ - Get current time in milliseconds, or HH:MM:SS:MMM format

I've written a c++ function to get the current time in HH:MM:SS format. How can I add milliseconds or nanoseconds, ... = sstm.str(); return s; } See Question&Answers more detail:os...

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

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372 views

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c++ - Why are designated initializers not implemented in g++

Is there any specific reason why has support for designated initializers not been added to g++? Is the reason that ... in the grammar of 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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