C++ Boost shared_ptr示例程序
我试图熟悉boost共享ptr。我遇到了下面的例子C++ Boost shared_ptr示例程序,c++,boost,foreach,shared-ptr,C++,Boost,Foreach,Shared Ptr,我试图熟悉boost共享ptr。我遇到了下面的例子 #include <vector> #include <set> #include <iostream> #include <algorithm> #include <boost/shared_ptr.hpp> /* The application will produce a series of * objects of type Foo which later must be
#include <vector>
#include <set>
#include <iostream>
#include <algorithm>
#include <boost/shared_ptr.hpp>
/* The application will produce a series of
* objects of type Foo which later must be
* accessed both by occurrence (std::vector)
* and by ordering relationship (std::set).
*/
struct Foo
{
int x;
Foo( int y ) : x(y)
{
}
~Foo()
{
std::cout << "Destructing a Foo with x=" << x << "\n";
}
};
typedef boost::shared_ptr<Foo> FooPtr;
struct FooPtrOps
{
bool operator()( const FooPtr & a, const FooPtr & b )
{
return true; //a->x > b->x;
}
void operator()( const FooPtr & a )
{
std::cout << a->x << "\n";
}
};
int main()
{
std::vector<FooPtr> foo_vector;
std::set<FooPtr,FooPtrOps> foo_set; // NOT multiset!
FooPtr foo_ptr( new Foo( 2 ) );
foo_vector.push_back( foo_ptr );
foo_set.insert( foo_ptr );
foo_ptr.reset( new Foo( 1 ) );
foo_vector.push_back( foo_ptr );
foo_set.insert( foo_ptr );
foo_ptr.reset( new Foo( 3 ) );
foo_vector.push_back( foo_ptr );
foo_set.insert( foo_ptr );
foo_ptr.reset ( new Foo( 2 ) );
foo_vector.push_back( foo_ptr );
foo_set.insert( foo_ptr );
std::cout << "foo_vector:\n";
std::for_each( foo_vector.begin(), foo_vector.end(), FooPtrOps() );
std::cout << "\nfoo_set:\n";
std::for_each( foo_set.begin(), foo_set.end(), FooPtrOps() );
std::cout << "\n";
return 0;
}
我想它只是想告诉你
4
对象被实例化,2
不同的容器每个都包含所有4
对象(即相同的4
对象),最后只有4
对象被销毁。还要注意FooPtrOps()
是默认构造的FooPtrOps对象。这就是传递到foreach
函数的内容。在foreach
内部,它调用operator()(const FooPtr&a)成员函数。@anomail-for_每个循环文档都指出第三个参数应该是lambda函数(不是对象?)@liv2hak文档声明它是一个模板类型,满足一元函数的要求(即,一个函数对象、一个函数和一个lambda都可以工作)。@liv2hak看到了。
foo_vector:
2
1
3
2
foo_set:
2
3
1
2
Destructing a Foo with x=2
Destructing a Foo with x=1
Destructing a Foo with x=3
Destructing a Foo with x=2