In the code below, static_assert operates on the addresses of local variables, but however MS compiles it and the assertion does not fail:
#include <tuple>
#include <string>
struct A
{
int a;
double b;
std::string c;
};
void f()
{
A a{ 1, 3.0, "abc" };
constexpr auto t1 = std::tie(a.a, a.b, a.c);
static_assert(&std::get<0>(t1) == &a.a);
}
Use the following command to compile this example:
cl /std:c++17 /EHsc a.cpp(more…)
Consider the following scenario: there where structure A in an old version of a C++ application:
struct A
{
double a;
int b;
std::string c;
};
An instance of A was serialized into a file in a binary format and after that the application was updated to a new version.
But in the new version of the application structure A was modified by adding fields d and e and deleting field a:
struct A
{
int b;
std::vector<int> d;
bool e;
std::string c;
};
and the new version of the application needs to deserialize an instance of its new structure A from the file containing old version of A.
(more…)I implemented a simple C++ binary serialization framework that makes a structure or class serializable by adding a macro that usually takes one line of code as shown in the example below:
struct A
{
bool x;
int y;
AWL_SERIALIZABLE(x, y)
};
There is also a macro that makes a structure or a class equatable:
AWL_MEMBERWISE_EQUATABLE(A)(more…)
The code below demonstrates how to parse GUID in C++ using a regular expression:
#include <iostream>
#include <string>
#include <regex>
int main()
{
static const std::wregex regex(L"[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}");
std::wstring sample = L"850fe1da-0ea6-c1a8-9810-0c1cece30698";
std::match_results<std::wstring::const_iterator> match;
if (std::regex_match(sample, match, regex))
{
std::wcout << L"matches" << std::endl;
}
else
{
std::wcout << L"does not match" << std::endl;
}
return 0;
}
(more…) For example, std::forward comes to play if I implement a template container with two ‘insert‘ function overloads that take the parameters of type const T & and T && respectively. I implement all the private insertion logic with T&&, but when I need to know the original value type passed to ‘insert‘ method I use std::forward as shown in the example below:
#include <iostream>
#include <string>
class Value
{
public:
Value(const char * sz) : m_s(sz)
{
}
Value(const Value & other) : m_s(other.m_s)
{
std::cout << "copy constructor: " << m_s << std::endl;
}
Value(Value && other) : m_s(std::move(other.m_s))
{
std::cout << "move constructor: " << m_s << std::endl;
}
const std::string & ToString() const
{
return m_s;
}
private:
std::string m_s;
};
(more…) The string representation of a type is implementation defined in C++, for example the following code produce the different output with MSVC, GCC and CLang:
#include <string>
#include <iostream>
struct A {};
class B {};
namespace ns
{
struct X {};
}
int main()
{
std::cout << typeid(A).name() << ", " << typeid(B).name() << ", " << typeid(ns::X).name() << ", " << typeid(std::string).name() << std::endl;
return 0;
}
(more…) We had a discussion with colleagues on why in the following code we cannot simply use
static_assert(false)
but need to do a trick with ‘always_false’:
#include <type_traits>
template<typename>
struct always_false : std::false_type {};
template<typename Type>
constexpr int Get()
{
if constexpr (std::is_same_v<Type, int>)
{
return 1;
}
else if constexpr (std::is_same_v<Type, bool>)
{
return 2;
}
else {
static_assert(always_false<Type>::value);
}
}
(more…) I installed Node.js and Vue.js cli with the following commands
npm install -g @vue/cli npm install -g @vue/cli-init
and a sample application with
vue init webpack-simple my-vue-app cd my-vue-app npm install npm run dev
Below I wrote down a simple PHP script that saves client IP address to a file. If the IP address of your home machine periodically changes, you can store it on a web server once a minute by scheduling a task like this:
sudo crontab -u <user> -e
* * * * * wget -q -O /dev/null -o /dev/null "https://yourwebsite.com/ip.php?rig=rig1&password=XXXXX"
where ip.php is the following PHP script:
(more…)
WIX bootstrapper application (BA) can easily determine if it runs as admin with the following code:
using System;
using System.Diagnostics;
using System.Security.Principal;
static bool IsAdmin()
{
WindowsIdentity id = WindowsIdentity.GetCurrent();
WindowsPrincipal principal = new WindowsPrincipal(id);
return principal.IsInRole(WindowsBuiltInRole.Administrator);
}
and if it does not, run a new instance as admin and exit:
static void RunAsAdmin()
{
ProcessStartInfo proc = new ProcessStartInfo
{
UseShellExecute = true,
WorkingDirectory = Environment.CurrentDirectory,
FileName = Process.GetCurrentProcess().MainModule.FileName,
Verb = "runas"
};
Process.Start(proc);
}