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…)
I installed Perl, downloaded and extracted OpenSSL 1.1.0h and built 64 bit version in VS2015 x64 Native Tools Command Prompt with the following commands:
set PATH=%PATH%;C:\Perl64\bin perl Configure VC-WIN64A no-asm nmake
32 bit version can be built with VC-WIN32 configuration option as described in INSTALL:
on Windows (only pick one of the targets for configuration):
$ perl Configure { VC-WIN32 | VC-WIN64A | VC-WIN64I | VC-CE }
$ nmake
$ nmake test
$ nmake install
probably ‘A’ suffix means AMD and ‘I’ means something else, so we need ‘A’.
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);
}
Once std::vector is filled (size() equals to capacity()), a subsequent push_back(…) results in an exponential expansion of the vector capacity. The following table shows that the expansion happens when the index reaches a power of two:
index: 0, capacity: 1, address: 0x1fa6c20 index: 1, capacity: 2, address: 0x1fa6c40 index: 2, capacity: 4, address: 0x1fa6c20 index: 4, capacity: 8, address: 0x1fa6c60 index: 8, capacity: 16, address: 0x1fa6c90 index: 16, capacity: 32, address: 0x1fa6ce0 index: 32, capacity: 64, address: 0x1fa6d70 index: 64, capacity: 128, address: 0x1fa6e80 index: 128, capacity: 256, address: 0x1fa7090 index: 256, capacity: 512, address: 0x1fa74a0 index: 512, capacity: 1024, address: 0x1fa7cb0 index: 1024, capacity: 2048, address: 0x1fa8cc0 index: 2048, capacity: 4096, address: 0x1faacd0 index: 4096, capacity: 8192, address: 0x1faece0 index: 8192, capacity: 16384, address: 0x1fb6cf0 index: 16384, capacity: 32768, address: 0x1fc6d00 index: 32768, capacity: 65536, address: 0x1fe6d10 index: 65536, capacity: 131072, address: 0x2026d20 index: 131072, capacity: 262144, address: 0x20a6d30 index: 262144, capacity: 524288, address: 0x21a6d40 index: 524288, capacity: 1048576, address: 0x23a6d50 index: 1048576, capacity: 2097152, address: 0x27a6d60 index: 2097152, capacity: 4194304, address: 0x2fa6d70 index: 4194304, capacity: 8388608, address: 0x7f8e9225f010 index: 8388608, capacity: 16777216, address: 0x7f8e8e25e010 index: 16777216, capacity: 33554432, address: 0x7f8e8625d010 index: 33554432, capacity: 67108864, address: 0x7f8e7625c010 index: 67108864, capacity: 134217728, address: 0x7f8e5625b010 index: 134217728, capacity: 268435456, address: 0x7f8e1625a010 index: 268435456, capacity: 536870912, address: 0x7f8d96259010 index: 536870912, capacity: 1073741824, address: 0x7f8c96258010
The following C++ code demonstrates how to erase an element a reverse iterator points to:
#include <iostream>
#include <set>
#include <vector>
#include <assert.h>
int main()
{
std::set<int> set;
set.insert(15);
std::cout << set.size() << " ";
auto ri = set.rbegin();
auto i1 = --ri.base();
auto i2 = --set.end();
assert(i1 == i2);
set.erase(i1);
std::cout << set.size() << std::endl;
}
The output is ‘0 1’. The key point here is that the reverse iterator is an adaptor for reverse-order traversal that can be created from forward iterator with std::make_reverse_iterator.
The following simple code C++ example can be used for investigation of how GCC thread sanitizer works:
#include <mutex>
#include <atomic>
#include <iostream>
#include <thread>
std::mutex mutex;
int a = 3;
const size_t size = 1000 * 1000;
std::atomic<int> b(1);
void testA()
{
for (size_t counter = 0; counter < size; counter++)
{
++b;
std::unique_lock<std::mutex> lock(mutex);
++a;
}
}
void testB()
{
for (size_t counter = 0; counter < size; counter++)
{
--b;
std::unique_lock<std::mutex> lock(mutex);
--a;
}
}
int main()
{
std::thread t1(testA);
std::thread t2(testB);
t1.join();
t2.join();
}
I wrote a sample application using OsgQtQuick that shows the Earth in two views:
with the following QML, that I copied from OsgQtQuick samples:
The code below demonstrates why it is not guaranteed that 4-byte value being written by another thread is read either as original or final, but it can be read “partially written”:
static constexpr int offset=2;
alignas(64) char vars[64+4-offset];
static volatile unsigned * const p = reinterpret_cast<unsigned *>(&vars[64-offset]);
unsigned getVar()
{
return *p;
}
void loop()
{
while(true)
{
*p = -1;
*p = 0;
}
}
#include <thread>
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <map>
int main()
{
std::thread thread(loop);
std::map<unsigned,int> xs;
for(int i=0;i<10000000;++i)
{
const auto x=getVar();
++xs[x];
}
for(const auto& x : xs)
std::cout << std::setfill('0') << std::setw(8) << std::hex << x.first << ": " << std::dec << x.second << " times\n";
std::exit(0); // exit, killing the thread without abnormal termination via std::terminate
}
Qt Quick Controls 2 does not support TableView and looks like they are not going to support it, some notable missing features from Qt Quick Controls 1 also are Action, SplitView and TreeView, so the following QML code would not work:
TableView {
TableViewColumn {
role: "time"
title: qsTr("date/time:")
width: parent.width - 30
}
TableViewColumn {
role: "score"
title: qsTr("result:")
width: 30
}
model: boardModel.list
ScrollIndicator.vertical: ScrollIndicator { }
}
But there is a solution with ListView, so there can be something like this:
In the following C++ code the values of ‘z’ and ‘n’ are undefined, because they are the result of an operation with signed integer arithmetic overflow (‘x’ and ‘y’ are first implicitly converted to signed int). The value of ‘w’ is implementation defined, because it is the result of a conversion:
#include <iostream>
#include <bitset>
int main(int argc, char *argv[])
{
unsigned short x = 65535, y = x;
unsigned short z = x * y;
unsigned int n = x * y;
std::cerr << "z = " << std::bitset<16>(z) << ", n = " << std::bitset<32>(n) << ", sizeof(int) = " << sizeof(int) << std::endl;
short w = 0x80000000;
return 0;
}
see Numeric conversions section of Implicit conversions article.