Recent questions tagged c++

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I need to create a 'red' image from a grayscale image. I am using this code: void build_red(const cv:: ... the number of channels is correct. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - What is the rationale to "no diagnostic required"?

Most people are familiar with the "undefined" and "unspecified" behaviour notes in C++, but what about " ... diagnostic required" type errors? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How do I deal with the system clock changing while waiting on a std::condition_variable?

I'm trying to implement some cross-platform code in C++11. Part of this code implements a semaphore object ... of working around this issue? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Should unsigned ints be used if not necessary?

Should one ever declare a variable as an unsigned int if they don't require the extra range of values? For example ... Java doesn't have them). See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How to disable OpenMP directives in a nice way?

I have C++ code with OpenMP pragmas inside. I want to test this code both for multithread mode (with OpenMP) ... way to enable / disable OpenMP? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - glGetAttribLocation returns -1 when retrieving existing shader attribute

I'm trying to pass in attributes to my vertex shader but for some reason it keeps giving me a -1 on the 3rd ... // 6 offset from beginning [..] See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Boost program options allowed set of input values

Is there a way to set an allowed set of input variables for parameters? For example parameter "arg" can have only ... like "cat" and "dog". See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - std::vector : cannot bind 'std::ostream {aka std::basic_ostream<char>}' lvalue to 'std::basic_ostream<char>&&'

I encountered a confusing error message when trying to do something as simple as std::cout << std::vector<int> ... how to interpret it? Thanks See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - What does ifstream::rdbuf() actually do?

I have the following code and it works pretty good (other than the fact that it's pretty slow, but I don't care ... 1; return 0; } Any insight? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - When should I use std::any

Since C++17 std::any is introduced. One can now write code like this #include <iostream> #include <any> #include ... //gcc.godbolt.org/z/-kepOD See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How do I avoid scientific notation for large numbers?

I am doing 2^1000 and I am getting this: 1.07151e+301 Is there any way to actually turn this into a proper ... way working with the e+301 part? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why does calling std::move on a const object call the copy constructor when passed to another object?

Why does calling std::move on a const object call the copy constructor when passed to another object? Specifically ... with respect to const. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - "delete this" in constructor

What actually happen when I execute this code? class MyClass { MyClass() { //do something delete this; } } See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Is comparison of const_iterator with iterator well-defined?

Consider the following code: #include <vector> #include <iostream> int main() { std::vector<int> vec{ ... and const_iterator be safely compared? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How can I get a pointer to the first element in an std::vector?

I want to write data from an std::vector<char> to a socket, using the write function, which has this prototype ... , while I need a pointer. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Deletion of copy-ctor & copy-assignment - public, private or protected?

In order to make an object non-copiable we can explicitly delete both its copy-constructor and copy-assignment ... choice make any difference? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How to perform a dynamic_cast with a unique_ptr?

I have a class hierarchy as follows: class BaseSession : public boost::enable_shared_from_this<BaseSession> class ... should be reference. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - What's the use of memset() return value?

memset() is declared to return void* that is always the same value as the address passed into the function. What ... does it not return void? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Finding common characters in two strings

I am coding for the problem in which we got to count the number of common characters in two strings. Main part of ... coding with an O(n) logic. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How to display OpenCV Mat on MFC View

I thought displaying OpenCV2 Mat on MFC View is simple but is not. This is only relevant material I found on google. ... .rgbReserved = 0; } } } See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How to use boost bisection?

Yesterday I had problems with another boost functions but luckily you guys helped me to solve them. Today I would need ... min+max/2? Thanks ! See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - "Manual" signature overload resolution

I want to make a std::function like object that can handle storing more than one overload. Syntax sort of ... ) ) {} template<typename... OtherSignatures> my_function& operator=...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why does ofstream("log.txt", ios::app|ios::trunc); always fail?

The following code was compiled with VC++ Nov 2012 CTP on Windows 7 x64. #include <fstream> using namespace std; ... ios::app and ios::trunc? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - constructing a Data Frame in Rcpp

I want to construct a data frame in an Rcpp function, but when I get it, it doesn't really look like a data frame. I've ... 2 4 2 1 2 2 4 6 8 2 See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Is there an easy way/algorithm to match 2 clouds of 2D points?

I am wondering if there is an easy way to match (register) 2 clouds of 2d points. Let's say I have an ... it is) anything is unclear. cheers See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Overloading reference vs const reference

I have the following code: #include <iostream> template <typename T> void f(T& x) { std::cout << "f( ... version unambiguously called for f(b)? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - What are static variables?

What are static variables designed for? What's the difference between static int and int? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How can I generate dense unique type IDs at compile time?

I'm trying to make a system of classes that are small objects, and the base class has a member that is a ... C++ has compile time reflection? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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