Recent questions tagged C++

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c++ cli - convert from std::string to String^

I have a function in C++ that have a value in std::string type and would like to convert it to String^. ... Hello World"); outValue = str; } 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++ - Standard container re-allocation multipliers across popular toolchains

Containers like std::basic_string and std::vector perform automatic re-allocations when internal capacity runs out. The ... aka φ) STLport: 2 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++ - Print an ASCII art diamond

This is a homework question I got for my programming course at school, and I'm kind of lost, so please help. Here ... cout << endl; } 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++ - The result of CreateCompatibleDC only has two colors

In the following code, anytime CreateCompatibleDC is called, the resulting device context only has two colors: black ... occurs. Any ideas? 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’s the best way to cast a function pointer from one type to another?

I've searched Stack Overflow for an answer, but I get nothing specific to this problem: only general cases about ... (very useful, actually). 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 binary to std::fstream using the << operator

For some reason this sort code is not working as I would expect: std::fstream theFile; theFile.open(< ... ships with Visual Studio 2010. 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++ - Timing of scope-based lock guards and return values

class C { mutable std::mutex _lock; map<string,string> deep_member; public: auto get_big_lump() { std:: ... (or actual!) optimizations? 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 valid to directly call a (virtual) destructor?

In this answer, Ryan directly calls the virtual destructor. I've tested the code in VS2010, and it correctly calls ... (this) MyClass(); call? 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++ - /Za compiler directive does not compile system headers in VS2010

I wanted to disable language extensions to be able to do some tests in my project. I found that I must set ... use system headers? Thanks 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++ - Class member without a default constructor

Suppose I have a class A without a default constructor, a factory method factoryA that returns an object of type A, ... = factoryA(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++ - OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cv:: cvtColor, file ........opencvmodulesimgprocsrccolor.cpp, line 3737

Hi I am trying to run this sample code from OpenCV: #include "opencv2opencv.hpp" using namespace cv; int ... appreciated. Thanks in advance! 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 I subtract memory addresses, why is the result smaller than I expected?

I have the following program: #include <iostream> struct X { int a; float b; } x[10], *p1, ... understanding subtraction of two addresses ? 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 on exotic hardware

There was a question like this before, in 2011: Exotic architectures the standards committees care about Now, I'd ... this type doesn't exist? 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 character set of a char literal guaranteed to be ASCII?

Coming from a discussion started here, does the standard specify values for characters? So, is '0' guaranteed to be 48? ... where '0' isn't 48? 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++ - A 'using' declaration with an enum

A using declaration does not seem to work with an enum type: class Sample{ public: enum Colour {RED, BLUE, ... : using sample::Colour::RED; 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++ - check if a c++11 feature is enabled in compiler with CMAKE

I'm developing a project with CMake. My code contains constexpr methods, that are allowed in Visual Studio 2015, ... understand 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++ - What does `invalid initialization of non-const reference` mean?

When compiling this code I get the following error: In function 'int main()': Line 11: error: invalid ... understand why? Can anyone explain? 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++ - sum of overlapping arrays, auto-vectorization, and restrict

Arstechnia recently had an article Why are some programming languages faster than others. It compares Fortran and C and mentions ... b[i]; } } 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++ - Handles Comparison: empty classes vs. undefined classes vs. void*

Microsoft's GDI+ defines many empty classes to be treated as handles internally. For example, (source ... cannot dereference the handles. 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 pass a temporary array?

How can I pass a temporary array? I want to do something like this: #include <iostream> int sum(int arr[]) { ... or const int&[] won't 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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663 views

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c++ - Distinguish zero and negative zero

I have run into a situation in my code where a function returns a double, and it is possible for this ... can I distinguish between the two? 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 has the destructor been called only once?

#include <iostream> using namespace std; class Test { public: Test() { printf("construct .. "); } ~Test() { ... /a.out construct .. destruct... 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 define is_iterator type trait?

I'm trying to code a is_iterator<T> type trait. Where when T is an iterator type is_iterator<T>::value = ... trait than the one displayed above? 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's wrong with this inline initialization of std::array?

Consider the following declaration: #include <array> struct X { //std::array<bool,3> arr={false,false, ... single braces in struct definition? 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++ - Sync is unreliable using std::atomic and std::condition_variable

In a distributed job system written in C++11 I have implemented a fence (i.e. a thread outside the worker ... fix this in a performant way? 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 my book's discussion of lambda return types wrong?

My book says this: Lambdas with function bodies that contain anything other than a single return statement that do ... 2.0 Thread model: posix 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++ - Skipping iterator

I have a sequence of values that I'd like to pass to a function that takes a (iterator begin, iterator ... the way the iteration advances. See Question&Answers more detail:os...

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

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217 views

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c++ - Casting to void* and Back to Original_Data_Type*

I have seen and used this many times is C++, specially in various thread implementations. What I wonder is if ... there are any? 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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