Questions tagged [c++]
C++ is a general-purpose programming language. Use this tag for questions about/utilizing C++. Do not also tag questions with [c] unless you have a good reason. C and C++ are different languages. Use a versioned tag such as [c++11], [c++20] etc. for questions specific to a standard revision.
809,426
questions
0
votes
0
answers
6
views
Very slow CPP color detection when checking for mass amounts of color pixels
So, I am creating a program where it counts of pure black pixels given an x,y range on the monitor. The only problem is that this method provided below takes so long to run, while in java, it can run ...
- 1
0
votes
0
answers
9
views
How to include version information in a C++ project?
I wrote a C++ static library, and I want to add version information for it in a designated header. I'm working with C++14.
I'm contemplating on multiple approaches:
Adding it as macros:
#pragma once
...
- 1
0
votes
0
answers
61
views
How to executing code before a process is launched?
I am currently working on a project where I need to execute some code before a certain process is launched.
I am not sure how to approach this problem and I was hoping someone could provide some ...
- 19
-2
votes
0
answers
27
views
Are STL containers assigned by copy? [duplicate]
Recently I have encountered some problems when reading the source code of MSVC STL thread, I am very confused about how thread implements parameter copy, he clearly uses a perfect forward, and perfect ...
- 1
0
votes
0
answers
10
views
How can I change camera view of MuJoCo simulation?
I am working on a robot simulation using a MuJoCo (ver.3.1.1) with C++ language.
And I am trying to change the default camera view of simulation, but I have a trouble in this work.
My project composed ...
0
votes
0
answers
17
views
Setup subdirs project with app and lib subprojects for qmake in QtCreator
I'm setting up a sample subdirs projectmain with two subprojects: projectgui (app template) and and projectsub1 (lib template). I'm using QtCreator 13.0.2 with Desktop Qt 6.7.2 MSVC201964bit kit on ...
- 386
0
votes
0
answers
27
views
error: no match for 'operator!=' (operand types are 'QVector<Object>' {aka 'QList<Object>'} and 'QList<Object>')
I have Qt code that looks like following:
class test_gadget {
Q_GADGET
Q_PROPERTY(QString test MEMBER test)
public:
QString test;
};
class test_gadget2 {
Q_GADGET
Q_PROPERTY(...
- 41
2
votes
1
answer
27
views
How to forward constructor parameters to a contained tuple when one of the tuple elements has a default constructor and another one doesn't [duplicate]
I am trying to write a class that uses a std::tuple to store a bunch of objects with potentially different types. If the elements all have ctors that take some parameter, I can initialize the tuple ...
- 313
0
votes
0
answers
20
views
How to use cudaMalloc and cudaMemcpy to allocate dynamic memory in a struct?
I try to use cudaMalloc and cudaMemcpy to allocate dynamic memory but meets Segmentation Fault error during running. I think I never allocate memory for double *data for device, but I don't know how ...
0
votes
0
answers
35
views
Why do flushing using std::endl when the buffer is not full [duplicate]
In C++, a newline could be printed using std::endl or adding a "\n" to the end of the printed text. Though in the latter case, the output buffer is not flushed until it is full, but this ...
0
votes
1
answer
28
views
Why does separating the interface and implementation of a `std::formatter` specialization cause constraints to fail?
I was trying to specialize std::formatter<T> for a basic custom type Vector3D, but I'm receiving a compiler error. Here is a minimal reproducible example:
vector.h defines the Vector3D class and ...
- 3,349
0
votes
0
answers
28
views
why cv::waitKey(x) is not closing frame after x seconds?
#include<opencv2/imgcodecs.hpp>
#include<opencv2/highgui.hpp>
#include<string>
int main()
{
std::string path = "wallpaperflare.jpg";
cv::Mat img=cv::imread(path);
...
- 37
-3
votes
0
answers
34
views
Setting values inside a tuple of vectors in a Singleton with std::get
I am creating a tuple of vectors of various objects - and it is a singleton. I have nested this singleton class within another class.
Right now I have no idea what the issue is, but I am unable to ...
0
votes
2
answers
43
views
C++ logical error: strstr function not finding an available entry
I wrote the code below to try the strstr() function to search for a name in a list, but it is not finding it.
Can someone please explain why this code fails to find the name I am trying to look for?
#...
0
votes
1
answer
94
views
Smallest element after xor
Starting with array of N positive integers, support Q queries. Each query contains a positive integer i. To answer the query, replace each element of the array with the result of xoring it with i, ...
- 136
1
vote
1
answer
88
views
Is it possible to initialize a struct reference with an array?
Is it possible to do something like this?:
struct S {
int length;
char data[100];
};
class C {
uint8_t buffer[10];
S& s = buffer[0];
};
If I use pointer it compiles, but working with ...
- 249
0
votes
0
answers
27
views
QT no matching function for call to 'makeCallableObject'
I'm trying to use the default Qfontcombobox in my qt app to change the font of a text edit, and i am getting this error for some reason.
Here is my definition for my mainwindow.cpp
#include "...
- 33
-3
votes
1
answer
52
views
Understanding usage of std::for_each with structs [duplicate]
I am trying to understand how below code works, from cpp reference website:
std::vector<int> v{3, -4, 2, -8, 15, 267};
struct Sum
{
void operator()(int n) { sum += n; }
int sum {0};
};
...
- 111
0
votes
1
answer
24
views
NCryptSignHash returns NTE_INVALID_PARAMETER (0x80090027)
I'm working with some old code that was signing data using an installed certificate and the CryptoAPI, and I need to migrate it to use CNG. I've tried two different approaches, one using ...
- 108
0
votes
0
answers
45
views
How should i set my .json files in vscode?
How should i set my .JSON files in my c++ directory:
task.JSON
launch.JSON
c_cpp_properties.JSON
settings.JSON
I'm using GCC.
My current configurations are:
1. launch.JSON
{
"configurations&...
- 1
0
votes
2
answers
104
views
How do interfaces solve the circle-ellipse problem?
It is sometimes said that interfaces solve several problems of object-oriented programming, in particular the circle-ellipse problem. It would be this interface
class IEllipse {
public:
virtual ...
- 3,216
-2
votes
1
answer
47
views
Access elements in list<vector<int>> without using temporary space
I had a query on how to access the elements in a list<vector<int>>, I can access the elements by assigning the values of the iterator into a temp vector. For example,
list<vector<int&...
0
votes
6
answers
87
views
C++ function template specialization based on the templated return type
In C++20, instead of doing
size_t count = 42;
std::vector<int> my_vector;
vec.reserve(count);
std::copy_n(std::istream_iterator<T>(std::cin), count, std::back_inserter(vec));
I want to be ...
- 243
0
votes
1
answer
45
views
Allowing STL algorithms to swap when iterators dereference to a wrapper class (i.e. an rvalue)
I am implementing a C++ wrapper for a C library that has a "vector of vectors" container. In the C++ interface, I would like iterators to dereference not to a raw C pointer, but to a ...
- 25.3k
-1
votes
0
answers
35
views
C++ removing LAST object from map causes program to terminate [duplicate]
I'm new to C++ and I'm working with some old C++ code. Below is a basic example of the code that is failing? There are some comments in the example code explaining the error. Basically when removing ...
0
votes
0
answers
34
views
Incorrect value of CMAKE_SYSTEM_PROCESSOR when using cibuildwheel and scikit-build-core on GitHub macos-14 runner
Below are demo files to reproduce the issue. I expect the value of CMAKE_SYSTEM_PROCESSOR should be arm64. However, it is x86_64. See line 1233 in the Build wheels section, which corresponds to the ...
- 527
-4
votes
2
answers
54
views
I was working on vs code in C++ and suddenly I got an error not showing any output in terminal [closed]
I was working on vs code in C++ and suddenly an error appeared that no output was shown in the terminal. I tried
Please help guys, because this error is hindering my work. I was working in oop on ...
0
votes
0
answers
16
views
Youtube LiveChatMessages resource caching with ETag not work
My app every 5s requests live chat messages for YouTube live stream api and to prevent unnecessary data transfers I'm also utilizing ETags.
const auto listLiveMessagesRequest = yt::api::live::...
0
votes
1
answer
47
views
Why is ARM NEON SIMD Sum is slower than serial sum?
I have been trying to benchmark memory bandwidth on my M2 Mac and one thing I noticed that when I try to use ARM NEON SIMD it seems that it has a slower processing time and lower memory bandwidth. ...
- 7,221
0
votes
0
answers
16
views
wxWidget frame / window not closing
I have been developing a custom UI for Autodesk Alias. I use wxwidget for this.
i follow youtube tutorials and made a window / frame.
i have problem now. when i click the close button in menubar ,the ...
0
votes
1
answer
32
views
Tooltip not appearing in FLTK custom widgets
I am creating a tool for a project using Fl_Tabs and some custom widget, which encompasses some other custom classes.
I would like to have a tooltip appearing when the mouse is hoovering on the custom ...
- 1,050
-2
votes
0
answers
39
views
Find Camera Location Using solvePnP [closed]
As part of a project I'm working on, I need to find a camera location using solvePnP.
The goal of this project is to find the position of the camera using solvePnP, and compare to the true camera ...
-7
votes
0
answers
39
views
Clarification about pointer to constant Foo where Foo is a struct [duplicate]
Code:
struct Foo
{
int a = 0;
int const b = 1;
};
int main()
{
Foo f{};
Foo const *const_ptr_f = &f;
const_ptr_f->a++; // error
}
// error: increment ...
0
votes
0
answers
29
views
how to fix this Error: qrc:/main.qml: No such file or directory
I'm developing a very basic QML GUI for a C++ project, but I'm having trouble adding file URLs to the program. I've tried using absolute paths, ./path, and ../path, but none of them work. Whenever I ...
2
votes
0
answers
35
views
Weird behavior dealing with c++ std::variant comparison and operator functions [duplicate]
I have been trying to make a game in Visual Studio using c++17, and I created a class type called ErrorType to represent all the error numeric values (nan, inf, etc). By using std::variant<long ...
- 69
0
votes
0
answers
29
views
Websocket from ESP32 to Python to slow
I am working on a project where I have Python server that's connected to an esp32 cam (AI Thinker) via a websocket.
The ESP32 cam constantly takes frames and sends them to the server, where they are ...
- 193
0
votes
1
answer
29
views
qt6apptestqt_debug_metatypes.json: illegal value
EDIT
My CMake file looks like this:
cmake_minimum_required(VERSION 3.16)
project(testqt VERSION 0.1 LANGUAGES CXX)
set(CMAKE_AUTOMOC ON)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
find_package(Qt6 6.4 ...
- 41
-6
votes
1
answer
88
views
find the index of first occurence in a string
class Solution {
public:
int strStr(string haystack, string needle) {
int pos = -1, i, j = 0;
for (i = 0; i < haystack.size(); i++) {
if (haystack[i] == needle[0]) {
pos = i;...
- 1
1
vote
1
answer
55
views
Calling a consteval function within if consteval causes error in non-constexpr context
The following code does not compile with g++ 14.1 or clang++ 18.1:
#include <type_traits>
consteval int
plusone(int n)
{
return n+1;
}
constexpr int
maybeplusone(int n)
{
if (std::...
- 4,322
0
votes
1
answer
23
views
JVM cannot find Agent_OnLoad in agent lib
I am coding a Java Agent library. However, the JVM cannot find Agent_OnLoad function even if I have explicitly exported it in my C++ code.
JNIEXPORT jint JNICALL
Agent_OnLoad(JavaVM* vm, char* ...
- 31
1
vote
1
answer
31
views
Unable to compile a QT app utilising PCL Visualizer due to missing VTK/MPI C component
I'm trying to build a demo QT application using the Point Cloud Library (PCL) and its provided visualiser component (#include <pcl/visualization/pcl_visualizer.h>). I'm using Cmake for the build ...
- 2,770
0
votes
0
answers
32
views
Sticky guidelines for QSplitter
I am trying to implement a snap-to-grid/snap-to-guideline functionality to a QSplitter.
The idea is:
Integer values are set onto the QSplitter (or possibly its parent widget or another ancestor) ...
- 3,603
-1
votes
0
answers
24
views
How to configure CLion to avoid build failed while running
I have written a simple program in CLion C++ that solves USACO 2016 February Contest, BRONZE, Problem 1. Milk Pails. However, as I tried to run it, I got the following error
ld: open() failed, errno=...
- 82
0
votes
0
answers
48
views
Templating CUDA
CUDA supports templates and that is nice, I have however problem with interplay with C++.
Let's say I have functions
template <typename T>
void CUDAZeroPad2D(dim3 threads,
...
- 610
-1
votes
0
answers
24
views
spellchecker with doublyLinkedBag [duplicate]
I have an assignment i am trying to write I keep getting this error:
Added: watermellon
Added to dictionary: watermellon
Added: pineapple
Added to dictionary: pineapple
Misspelled word: apple
...
0
votes
0
answers
36
views
Huge slowdown when specifying `target_file_name` with the same directory as `target`
auto sink = boost::log::add_file_log(
boost::log::keywords::auto_flush = true,
boost::log::keywords::enable_final_rotation = false,
boost::log::keywords::file_name = logDir / (name + "...
0
votes
0
answers
23
views
Ceres-Solver-does the initial reference 3D point matter? Experiencing significantly high reprojection error
So I have a set of 2d-3d correspondence points where the 2d coordinate points are detected by a corner detection algorithm (not written by me, and verified to be correct) and 3d coordinate points ...
- 73
0
votes
0
answers
30
views
Calling methods from array of method pointers not executing [duplicate]
This doesn't execute any suggestions:
void (CClient::*pMethod[CNetwork::ClientEvent::E_CE_MAX_EVENTS])();
pMethod[CNetwork::ClientEvent::E_CE_ACCEPTED] = &CClient::Accepted;
pMethod[CNetwork::...
- 93
0
votes
0
answers
48
views
Unable to properly use Visual Studio Code for C++ Coding [closed]
Some Backstory and Info:-
This is my first time using Stack Overflow. So I may be inefficient in describing my issues, I apologize for that.
I mainly use C++, and also know C and Python.
I am a ...
0
votes
0
answers
72
views
C++ Rule of Zero with guaranteed/C ABI
I love and often use C++ Rule of Zero, but now there's a use case where I find it challenging to use.
I have 2 libraries, both maintained separately and even compiled with different compilers to ...
- 6,569