我正在编写一个性能关键型应用程序,我在其中创建大量类似类型的对象来下订单.我使用boost :: singleton_pool来分配内存.最后我的班级看起来像这样.
class MyOrder{
std::vector<int> v1_;
std::vector<double> v2_;
std::string s1_;
std::string s2_;
public:
MyOrder(const std::string &s1, const std::string &s2): s1_(s1), s2_(s2) {}
~MyOrder(){}
static void * operator new(size_t size);
static void operator delete(void * rawMemory) throw();
static void operator delete(void * rawMemory, std::size_t size) throw();
};
struct MyOrderTag{};
typedef boost::singleton_pool<MyOrderTag, sizeof(MyOrder)> MyOrderPool;
void* MyOrder:: operator new(size_t size)
{
if (size != sizeof(MyOrder))
return ::operator new(size);
while(true){
void * ptr = MyOrderPool::malloc();
if (ptr != NULL) return ptr; …我有一个Java Set,其中包含一些Integer元素.我想用Java 8流来汇总它的元素.
Set<Integer> numbers = new HashSet<>();
// Some code that will populate numbers
int sum = numbers.stream().mapToInt(Integer::intValue).sum() //Can overflow!
我可以用上面的代码来获得的总和,但内容numbers是Integer元素远低于Integer.MAX_VALUE并且有大量的人,使得它们的总和可能溢出.如何将Integer元素流转换为元素流Long并将其安全地求和？
我正在使用Boost asio编写一个应用程序,其中客户端和服务器交换使用google proto-buffers序列化的消息.我不知道通过网络发送的序列化消息的大小是多少.似乎proto-buf对象没有任何分隔符.
以下是.proto文件的内容.
package tutorial;
message Person {
required string name = 1;
required int32 id = 2;
optional string email = 3;
}
这是我从服务器写的方式
tutorial::Person p;
p.set_name("abcd pqrs");
p.set_id(123456);
p.set_email("abcdpqrs@gmail.com");
write(p);
boost::asio::streambuf b;
std::ostream os(&b);
p.SerializeToOstream(&os);
boost::asio::async_write(socket_, b,
boost::bind(&Server::handle_write, this,
boost::asio::placeholders::error));
在客户端我正在使用boost :: asio :: async_read读取上面发送的消息.如何在下面的代码中找出arg要设置为参数的值boost::asio::transfer_at_least？
boost::asio::async_read(socket_, response_,
boost::asio::transfer_at_least(arg),
boost::bind(&Client::handle_read_header, this,
boost::asio::placeholders::error));
或者,如何在读取整个对象后确保boost :: async_read返回？
我为MyOrder类编写了自定义运算符new和operator delete.我使用boost :: singleton pool分配内存.这是测试性能的程序,
#include <boost/pool/singleton_pool.hpp>
#include <boost/progress.hpp>
#include <iostream>
#include <new>
#include <vector>
class MyOrder{
std::vector<int> v1_;
std::vector<double> v2_;
std::string s1_;
std::string s2_;
public:
MyOrder(std::string s1, std::string s2): s1_(s1), s2_(s2) {}
~MyOrder(){}
static void * operator new(size_t size);
static void operator delete(void * rawMemory) throw();
};
struct MyOrderTag{};
typedef boost::singleton_pool<MyOrderTag, sizeof(MyOrder)> MyOrderPool;
void* MyOrder:: operator new(size_t size)
{
if (size != sizeof(MyOrder))
return ::operator new(size);
while(true){
void * ptr = MyOrderPool::malloc();
if (ptr != NULL) return ptr;
std::new_handler …I am trying to run the following test program on my Solaris 10 sparc machine using gcc 5.5.0
#include <iostream>
#include <cmath>
int main()
{
std::cout << "exp2(4) = " << std::exp2(4) << '\n'
<< "exp2(0.5) = " << std::exp2(0.5) << '\n'
<< "exp2(-4) = " << std::exp2(-4) << '\n';
return 0;
}
Here are the OS details,
~$ uname -a
SunOS sovms577 5.10 Generic_147147-26 sun4v sparc SUNW,SPARC-Enterprise-T5220
~$ cat /etc/release
Oracle Solaris 10 1/13 s10s_u11wos_24a SPARC
Copyright (c) 1983, …在下面的代码中,我抛出一个int,将其作为const int&捕获,重新抛出它并再次捕获它将其作为int&捕获.
#include <iostream>
int main()
{
try
{
try
{
int x = 1;
throw x;
}
catch(const int& e)
{
std::cout << "Inner catch" << std::endl;
throw;
}
}
catch(int & e1)
{
std::cout << "Outer catch" << std::endl;
}
return 0;
}
上述程序编译成功并打印
Inner catch
Outer catch
另一方面,下面的程序,我试图初始化一个int和一个const int,甚至不会编译.
#include <iostream>
int main()
{
int x = 0;
const int& y = x;
int& z = y
return 0;
}
我按预期得到以下错误
binding ‘const int’ to reference of …我使用boost::unordered_map如下
typedef boost::shared_ptr<WriterExeciter> PtrWriter;
typedef std::list<PtrWriter> PtrList;
boost::unordered_map<std::pair<unsigned int, unsigned long long>, PtrList> Map
Map instrMap;
现在我正在对PtrList循环中的类型列表进行一些更改
for(auto it = instrMap.begin(); it != instrMap.end(); ++it)
{
auto key = it->first();
auto list& = it->second();
//Make some change to an element in list
if(list.empty())
{
instMap.erase(key);
}
}
对列表进行更改是否会使instrMap的迭代器失效？
擦除元素将使指向擦除元素的迭代器无效.如何修改我的代码,以便这不会导致任何问题？使用it++而不是++it帮助？
谢谢
我正在学习使用Boost ASIO.以下是从Boost ASIO文档中提供的聊天示例中复制的一些代码,
typedef std::deque<chat_message> chat_message_queue;
class chat_client
{
public:
chat_client(boost::asio::io_service& io_service,
tcp::resolver::iterator endpoint_iterator)
: io_service_(io_service),
socket_(io_service)
{
boost::asio::async_connect(socket_, endpoint_iterator,
boost::bind(&chat_client::handle_connect, this,
boost::asio::placeholders::error));
}
void write(const chat_message& msg)
{
io_service_.post(boost::bind(&chat_client::do_write, this, msg));
}
void close()
{
io_service_.post(boost::bind(&chat_client::do_close, this));
}
private:
void handle_connect(const boost::system::error_code& error)
{
//Implementation
}
void handle_read_header(const boost::system::error_code& error)
{
//Implementation
}
void handle_read_body(const boost::system::error_code& error)
{
//Implementation
}
void do_write(chat_message msg)
{
bool write_in_progress = !write_msgs_.empty();
write_msgs_.push_back(msg);
if (!write_in_progress)
{
boost::asio::async_write(socket_,
boost::asio::buffer(write_msgs_.front().data(),
write_msgs_.front().length()),
boost::bind(&chat_client::handle_write, this, …我正在填充一个Map<Character, Integer> alphabetToNumber映射与其字母位置对应的字母
char [] alphabetArray = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
Map<Character, Integer> alphabetToNumber = new HashMap<>();
int counter = 1;
for(Character letter : alphabetArray) {
alphabetToNumber.put(letter, counter);
counter++;
}
上面的代码有效,但我想知道是否可以使用Java 8流完成.谢谢.
#include <iostream>
class A
{
public:
A()
{
std::cout << "A()" << std::endl;
}
virtual ~A()
{
std::cout << "~A()" << std::endl;
}
};
class B:public A
{
public:
B()
{
throw std::exception();
std::cout << "B()" << std::endl;
}
~B()
{
std::cout << "~B()" << std::endl;
}
};
int main()
{
try
{
B b;
}
catch(std::exception & e)
{
}
return 0;
}
上面的代码输出,
A()
~A()
抛出异常时,已创建B.那么为什么B的析构函数不被称为？
在下面的代码中,我正在创建一个producer thread并n consumer threads从每个专用queue和打印到的读取stdout.这段代码有时会在声明中崩溃consumerQueues[id]->empty().通过调试去我看到consumerQueues[id]是0x0当它崩溃.现在在init()函数中,我在创建worker 之前创建了ith使用者.我不确定为什么会留下来.请帮我弄清楚发生了什么.queueiththreadconsumerQueues[id]0x0
#include <thread>
#include <queue>
#include <memory>
#include <iostream>
#include <mutex>
#include <condition_variable>
class Test
{
private:
void producer()
{
while(true)
{
std::string s = "abc";
for(const auto& q : consumerQueues)
{
std::unique_lock<std::mutex> lock(mutex);
q->push(s);
condition_variable.notify_all();
}
}
}
void consumer(int id)
{
while (true)
{
std::string job;
{
std::unique_lock<std::mutex> lock(mutex);
while(consumerQueues[id]->empty())
{ …c++ ×9
boost ×2
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exception ×2
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java-stream ×2
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