boost 学习(1)

智能指针的学习

中文教程网站 http://zh.highscore.de/cpp/boost/

不过代码可能由于BOOST 版本不同需要稍作修改

scoped_ptr 离开作用域则自动调用类析构函数或者函数delete方法

shared_ptr 使用率最高的指针类似scoped_ptr 但是所有权可以转移

#include <iostream>
#include <vector>
#include <windows.h>
#include <boost/smart_ptr.hpp>
 
using namespace std;
 
class CHandle
{
    HANDLE hProcess;
public:
    CHandle() { hProcess = OpenProcess(PROCESS_SET_INFORMATION, FALSE, GetCurrentProcessId()); }
    ~CHandle() { cout << "Enter destructor handle" << endl; if(NULL != hProcess){CloseHandle(hProcess);hProcess = NULL;} }
    void PrintHandle() {cout << hProcess << endl;}
};
 
 
int _tmain(int argc, _TCHAR* argv[])
{
    {
        boost::scoped_ptr<CHandle> sp(new CHandle);
        sp->PrintHandle();
        sp.reset(new (CHandle));
        sp->PrintHandle();
    }
    cout << endl;
     
    typedef boost::shared_ptr<int> SHP;
    vector<SHP> v;
    v.push_back(SHP (new int(1)));
    v.push_back(SHP (new int(2)));
    v.push_back(SHP (new int(3)));
 
    for(vector<SHP>::iterator it = v.begin();
        it != v.end();++it)
    {
        cout << *(*it) << endl;
    }
    cout << endl;
     
    boost::shared_ptr<int> i1(new int(99)); 
    boost::shared_ptr<int> i2(i1);   
    cout << *i1 << endl;
    cout << *i2 << endl;
 
    i1.reset(new int(5));  
    cout << *i1 << endl;
    cout << *i2 << endl;
 
     
 
    return 0;
}

再来一个示例

智能指针创建空间保存输入的字符串

int _tmain(int argc, _TCHAR* argv[])
{
    char sz[] = "this is  test string";
    int strLen = strlen(sz) + 1;
    typedef boost::shared_ptr<char> SHPCHAR;
    SHPCHAR szp(new char[strLen]);
    strncpy(szp.get(),sz,strLen);
 
    cout << szp.get() <<endl;
     
 
    return 0;
}

// boost  filsystem 库练习
#include "stdafx.h"
#include <iostream>
#include <vector>
#include <windows.h>
#include <boost/smart_ptr.hpp>
#include <boost/function.hpp>
#include <boost/signal.hpp>
#include <string>
#include <boost/thread.hpp>
#include <stdlib.h>
 
#define BOOST_FILESYSTEM_VERSION    2
#include <boost/filesystem.hpp>
 
using namespace std;
 
 
 
int _tmain(int argc, _TCHAR* argv[])
{
    boost::filesystem::path p("C:\\Windows\\System"); 
    std::cout << p.root_name() << std::endl; 
    std::cout << p.root_directory() << std::endl; 
    std::cout << p.root_path() << std::endl; 
    std::cout << p.relative_path() << std::endl; 
    std::cout << p.parent_path() << std::endl; 
    std::cout << p.filename() << std::endl; 
  
  
    boost::filesystem::path p1("photo.jpg"); 
    std::cout << p1.stem() << std::endl; 
    std::cout << p1.extension() << std::endl; 
 
    for (boost::filesystem::path::iterator it = p.begin(); it != p.end(); ++it) 
        std::cout << *it << std::endl; 
 
    boost::filesystem::path p2("C:\\"); 
    try
    { 
        boost::filesystem::file_status s = boost::filesystem::status(p2); 
        std::cout << boost::filesystem::is_directory(s) << std::endl; 
    } 
    catch (boost::filesystem::filesystem_error &e) 
    { 
        std::cerr << e.what() << std::endl; 
    } 
 
 
    return 0;
}

根据muduo开源库作者陈硕的一些文章。对于多线程下C++编程提出了一些观点。主要是多线程下对象的销毁比较困难，但是由于多线程下，mutext是无法保护析构的。而后提出了智能指针的方案并对使用该指针会遇到的困难和陷阱予以说明并提出解决方案。

该作者博客

http://www.cppblog.com/Solstice/

这里主要说说shared_ptr,采用计数方案，计数为零则自动删除对象，不必自己调用delete。可以使用unique()及user_count()判断该指针是否唯一指针获取者，以及指针计数。

示例如下:

#include <iostream>
#include <memory>
#include <string>
#include <set>
#include <map>
#include <boost/smart_ptr.hpp>
#include <assert.h>

using std::set;
using std::string;
using std::cout;
using std::endl;
using std::map;
using std::pair;

int main()
{
    boost::shared_ptr<int> num(new int(77));

    cout << "num: " << *num << endl;

    cout << "use_count: " << num.use_count() << endl;

    assert( num.unique());

    cout << "is unique() " << num.unique() << endl;

    boost::shared_ptr<int> num2 = num;

    cout << "use_count: " << num.use_count() << endl;
    cout << "use_count2: " << num2.use_count() << endl;

    boost::shared_ptr<int> spi = boost::make_shared<int>(78);
    cout << endl;
    cout << "make_shared " << *spi << endl;

    return 0;
}

与auto_ptr比较 , shared_ptr可以在容器中使用

#include <iostream>
#include <string>  
#include <boost/smart_ptr.hpp>
#include <vector>

using std::string;
using std::cout;
using std::endl;
using std::vector;
using boost::shared_ptr;
using boost::make_shared;

int main()
{
    typedef vector<shared_ptr<int> > v_sp;
    v_sp v(3);

    int i = 0;
    for(v_sp::iterator pos = v.begin(); pos != v.end(); ++pos)
    {
        (*pos) = make_shared<int>(++i); 
    }

    for(v_sp::iterator pos = v.begin(); pos != v.end(); ++pos)
    {
        cout << "value: " << *(*pos) << endl; 
        cout << "use_count: " << (*pos).use_count() << endl;
        cout << endl;
    }

    cout << endl;

    shared_ptr<int> p(v[1]);
    cout << "value: " << *p << endl;
    cout << "use_count: " << p.use_count() << endl; // 此刻有两个shared_ptr指向该值

    return 0;
}

创建智能指针的时候可以指定释放函数

#include <boost/shared_ptr.hpp> 
#include <iostream>
#include <windows.h> 

using namespace std;

HRESULT MyCloseHandle(HANDLE hHandle )
{
    cout << "Enter CloseHandle func" << endl;
    return CloseHandle(hHandle);
}


int main() 
{ 
    cout << "Start create shared_ptr for handle " << endl;
    boost::shared_ptr<void> h(OpenProcess(PROCESS_SET_INFORMATION, FALSE, GetCurrentProcessId()), MyCloseHandle);
    cout << "Create shared_ptr for handle finish" << endl;
    SetPriorityClass(h.get(), HIGH_PRIORITY_CLASS); 
}

示例：线程库的基本用法线程和线程组以及JOIN函数

#include <iostream>
#include <string>
#include <assert.h>
#include <vector>
#include <algorithm>

#include <boost/thread.hpp>
#include <boost/chrono.hpp>

using namespace std;
using namespace boost;

void print(int n)
{
    cout << "hello world: " << n << endl;
}

void print1(int n)
{
    cout << "hello world : " << n << endl;
}
void print2(int n)
{
    cout << "hello world : " << n << endl;
}
void print3(int n)
{
    cout << "hello world : " << n << endl;
}



int _tmain(int argc, _TCHAR* argv[])
{
    thread t(print,7);
    t.join();

    thread_group thread_grp;
    //===================================================
    thread_grp.create_thread(bind(print1,12));
    thread_grp.create_thread(bind(print2,22));
    thread_grp.create_thread(bind(print3,32));

    thread_grp.join_all();
    //===================================================



    return 0;
}