#include <iostream>
#include <memory>
#include <string>
#include <vector>
struct IObject {
virtual ~IObject() = default;
/// Returns the name of the object.
virtual std::string getName() const = 0;
/// Prints a textual description of the object.
virtual void describe() const = 0;
/// Eats another object.
virtual bool eat(IObject* other) = 0;
};
Category Archives: C++
An Interface Segregation Principle (ISP) example
An investigation of why dynamic_cast violates LSP
Signal sender cast in QT
QT implies that the client code will do qobject_cast that is actually dynamic_cast:
awl::ProcessTask<void> MarketModel::coPlaceOrder(OrderPtr p)
{
// Update SQLite databse...
// ...
// QT signals are used in both C++ and QML.
// They works with QObject*, and they are not aware of concrete types.
QObject::connect(p.get(), &OrderModel::statusChanged, this, &MarketModel::onOrderStatusChanged);
}
Examples of const function parameters in C++
Examples with int
Compiles without warnings with MSVC:
class A
{
public:
void f(const int a);
};
void A::f(int a)
{
a = 10;
std::cout << a;
}
Investigating cobalt::generator
Standard C++ generator
The code below demonstrates how standard C++23 synchronous generator works:
#include <boost/cobalt.hpp>
#include <iostream>
#include <generator>
namespace cobalt = boost::cobalt;
std::generator<int> numbers()
{
for (int i = 1; i <= 5; ++i)
{
co_yield i;
}
}
Building boost::cobalt with MSVC 2022
cd C:\dev\repos\boost_1_89_0
set OPENSSL_ROOT_DIR=C:/dev/libs/OpenSSL
set OPENSSL_USE_STATIC_LIBS=ON
bootstrap.bat
b2 cxxstd=20 install --with-system --with-thread --with-cobalt --prefix=C:/dev/libs/boost_1_89_0 --toolset=msvc-14.3 -s _WIN32_WINNT=0x0A00 link=static runtime-link=static variant=release address-model=64
b2 cxxstd=20 install --with-system --with-thread --with-cobalt --prefix=C:/dev/libs/boost_1_89_0 --toolset=msvc-14.3 -s _WIN32_WINNT=0x0A00 link=static runtime-link=static variant=debug address-model=64
An example of using base iterator in C++
The code below demonstrates how to access underlying range iterator by transformed iterator:
struct A
{
int x;
};
struct B
{
A* a;
};
std::vector<B> v;
int main()
{
auto a_range = v | std::views::transform(std::mem_fn(&B::a));
auto i = std::ranges::find(a_range, 5, std::mem_fn(&A::x));
A* a = *i;
B& b = *(i.base());
}
Move assignment operator in C++
Implicitly-declared move assignment operator
If no user-defined move assignment operators are provided for a class type, and all of the following is true:
- there are no user-declared copy constructors;
- there are no user-declared move constructors;
- there are no user-declared copy assignment operators;
- there is no user-declared destructor,
(more…)
Version tolerant serialization in C++
Last time I have been working on a C++ binary serialization framework that allows to serialize simple data structures with a few lines of code. First, you add AWL_REFLECT macro to all your structures as follows:
#include "Awl/Reflection.h"
#include <string>
#include <vector>
#include <set>
struct A
{
int a;
bool b;
std::string c;
double d;
AWL_REFLECT(a, b, c, d)
};
What is the type of a string literal in C++?
The code below compiles and the asserts do not fail:
#include <iostream>
int main()
{
auto a = "str";
const auto& ar = "str";
const char* b = "str";
auto const &c = a;
auto* d = &a;
const auto e = 2;
static_assert(std::is_same_v<const char(&)[4], decltype("str")>);
static_assert(std::is_same_v<const char*, decltype(a)>);
static_assert(std::is_same_v<const char(&)[4], decltype(ar)>);
static_assert(std::is_same_v<const char* const&, decltype(c)>);
static_assert(std::is_same_v<const char**, decltype(d)>);
static_assert(std::is_same_v<const int, decltype(e)>);
std::cout << "a: " << typeid(a).name() << std::endl;
std::cout << "ar: " << typeid(ar).name() << std::endl;
std::cout << "b: " << typeid(b).name() << std::endl;
return 0;
}
And a and b have identical typeids.
An example of overloading operator << in C++
The code below is compiled successfully with both GCC and MSVC:
#include <iostream>
#include <sstream>
template <class C>
class basic_format
{
public:
template <typename T>
basic_format & operator << (const T & val)
{
out << val;
return *this;
}
std::basic_string<C> str() const { return out.str(); }
operator std::basic_string<C>() const { return str(); }
private:
std::basic_ostringstream<C> out;
};
