Question

说我有以下代码：

controller.hpp

#include "testing.hpp"
#include <boost/shared_ptr.hpp>
class controller
{
    public:
        controller(void);
        void test_func (void);
        boost::shared_ptr <testing> _testing;
}

controller.cpp

#include "controller.hpp"
controller::controller() {
    boost::shared_ptr <testing> _testing (new testing);
    std::cout << _testing->test_bool << std::endl;
}

void controller::test_func (void) {
    // how to use _testing object?
    std::cout << _testing->test_bool << std::endl;

    return;
}

int main (void) {
    controller _controller;    // constructor called
    test_func();
    return 0;
}

testing.hpp

class testing
{
    public:
        bool test_bool = true;
}

我是否正确使用shared_ptr作为班级成员？课程controller中的多个功能需要使用_testing对象，我不想要testing课程＆＃39;每次指针超出范围时调用的构造函数/解构函数。也许这个不可能＆＃39;我应该避免，我开始意识到。

Answer 1

测试对象在控制器构造函数中构造，并在超出范围时被破坏。

只需：

__consumer_offsets

[已编辑]与问题所有者编辑相匹配

Answer 2

我冒昧地重写代码来演示共享指针的用法。通常使用它是因为一个对象可以同时在两个地方，四处移动，并且自动销毁。

#include <iostream>
#include <boost/shared_ptr.hpp>
#include <boost/make_shared.hpp>

class testing
{
public:
    std::string str;
    testing( const char* in ) : str( in ) { }
};
typedef boost::shared_ptr <testing> SP_testing;

class controller
{
public:
    controller( const char* in );
    void test_func ( );
    SP_testing _testing;
};

controller::controller( const char* in )
    :_testing( boost::make_shared< testing >( in ) )
{
    std::cout << "controller constructor: \"" << _testing->str << '\"' << std::endl;
}

void controller::test_func (void) {
    std::cout << "test_func: \"" << _testing->str << "\"  - cnt: " << _testing.use_count( ) << std::endl;
}

int main (void)
{
    //yet to be used shared pointer
    SP_testing outsider;
    {
        //this will create an instance of testing.
        controller _controller( "this is a test" ); // constructor called, prints
        outsider= _controller._testing;             //assign shared pointer
        _controller.test_func( );                   // test called, prints usage count.

    }//leaving scope, _controller will be destroyed but the _testing it created will not

    std::cout << "outsider: \"" << outsider->str << "\"  - cnt: " << outsider.use_count( ) << std::endl;

    //now testing will get destroyed.
    return 0;
}

上面，'outsider'指向controller::_testing。在test_func，它们都有一个指向同一对象的指针。即使控制器创建了测试对象，它也不会在控制器被破坏时被破坏。当出现这种情况时非常方便。此代码可以粘贴到一个.cpp文件中。感谢@DanMašek领导make_shared

在类对象上增加shared_ptr

2 个答案: