std::unordered_set has a template find function in C++20. To make it work I define a custom hash and a custom equality compares as follows:
struct BotSettings
{
std::string type;
std::string name;
bool started;
};
Category Archives: Programming languages
An example of heterogeneous lookup with std::unordered_set in C++20
Array subscript -N is outside array bounds warning in GCC11
Consider the code below with UB:
template <class Derived>
class A
{
public:
Derived * get() { return static_cast<Derived *>(this);}
private:
int m_a;
};
class B
{
public:
double m_b;
};
class X : public B, public A<X>
{
public:
int m_x;
};
int main()
{
A<X> a;
std::cout << a.get();
return 0;
}
Compiling Awl on Ubuntu 18 and 20 with GCC 11
Below I provided the instruction on how to build Awl on Ubuntu 18 and 20.
On Ubuntu 18 you do an extra step to install CMake version >= 3.12:
wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | sudo apt-key add -
sudo apt-add-repository 'deb https://apt.kitware.com/ubuntu/ bionic main'
sudo apt update
Then do the following steps on both Ubuntu 18 and 20:
sudo apt install cmake
cmake --version
C++ tasks from Yandex
Task 1
At an interview I was asked how to by a given vector of integers build resulting vector containing the products of all the elements except current. Below I provided my solution in C++:
#include <vector>
#include <iostream>
using V = std::vector<int>;
V func(const V& v)
{
V result;
result.resize(v.size());
int product = 1;
for (size_t pos = 0; pos != v.size(); ++pos)
{
result[pos] = product;
int a = v[pos];
product *= a;
}
Range-based for loop with universal reference.
It is possible to iterate over std::vector with &&:
#include <vector>
class A {};
int main()
{
std::vector<A> vec;
for (auto&& v : vec)
{
static_cast<void>(v);
}
return 0;
}
Links:
An annoying question about auto in C++
I was recently asked during a C++ job interview what are the types of riN variables in the code below:
int val = 25;
int foo() { return val; }
int& foo1() { return val; }
//warning: type qualifiers ignored on function return type
/*const*/ int foo2() { return val; }
const int& foo3() { return val; }
int main()
{
auto ri = foo();
auto ri1 = foo1();
auto ri2 = foo2();
auto ri3 = foo3();
//cannot bind non-const lvalue reference of type 'int&' to an rvalue of type 'int'
//auto& ri4 = foo();
auto& ri5 = foo1();
//cannot bind non-const lvalue reference of type 'int&' to an rvalue of type 'int'
//auto& ri6 = foo2();
auto& ri7 = foo3();
auto&& ri8 = foo();
auto&& ri9 = foo1();
auto&& ri10 = foo2();
auto&& ri11 = foo3();
return 0;
}
auto ignores the type qualifiers and references, so looks like the types are simply int, int& and int&&.
Negating the minimal integer results in an overflow in C++
The code below compiles with a warning:
#include <iostream>
#include <limits>
#include <cstdint>
int main()
{
int64_t m1 = -std::numeric_limits<int64_t>::min();
int64_t m2 = -m1;
std::cout << m1 << std::endl << m2 << std::endl << std::numeric_limits<int64_t>::max() << std::endl;
return 0;
}
Dragging a link from a browser to a QML app
When a link is dragged from a browser on Window 10 platform it contains the page title, but they did not make it accessible in QML:
import QtQuick 2.15
import QtQuick.Controls 2.15
ApplicationWindow {
visible: true
width: 640
height: 480
title: qsTr("Scroll")
id: root
DropArea {
id: dropArea;
anchors.fill: parent
onEntered: {
root.color = "gray";
drag.accept (Qt.LinkAction);
}
The sum of signed and unsigned is unsigned in C++
#include <iostream>
template <typename T>
void PrintValue(T val)
{
if constexpr (std::is_signed_v<T>)
{
std::cout << "signed";
}
else
{
std::cout << "unsigned";
}
std::cout << std::endl << val << std::endl;
}
None of C++ compilers have heterogeneous lookup for unordered containers except MSVC
At 10/20/2020:
And std::vector is not constexpr yet:
And there is no text formatting also.
Coroutines:
std::chrono::days:
