初始化 shared_ptr ,当对象需要默认构造函数时 [英] Initialising shared_ptr , when the object requires a default constructor
问题描述
为了将 shared_ptr 分配给柠檬图形库中的图形类型变量,我这样做了:
For assigning shared_ptr to a Graph type variable in lemon graph library i did this:
typedef ListDigraph Graph;
typedef std::shared_ptr<Graph> Process_pointer;
Process_pointer process(new Graph);
它工作正常,但现在我需要为地图对象声明一个 shared_ptr,通常地图对象的工作方式如下:
It worked fine, but now i need to declare a shared_ptr for a map object, Normally the map object works like this :
Graph process;
typedef ListDigraph::NodeMap<string> Node_names;
Node_names name(process);
也就是说,name 的默认构造函数需要一个 Graph 对象.
That is, name requires a Graph object for its default constructor.
为了为它声明一个 shared_ptr,我这样做了:
For declaring a shared_ptr for it, i did this:
typedef ListDigraph::NodeMap<string> Node_names;
typedef std::shared_ptr<Node_names> Nname_pointer;
Nname_pointer name = new Node_names;
name(process);
我知道,name 的声明是错误的,但是我如何为其分配内存以及使用进程对象对其进行初始化.
I know, the declaration for name is wrong, but how do i assign it memory as well as initialise it with process object.
推荐答案
auto p = std::make_shared<Node_names>(process);
这适用于具有任意数量参数的构造函数的类型.
This works for types with constructors with an arbitrary number of parameters.
请注意,这是使用托管对象创建 shared_ptr
的推荐默认方式.参见 为什么你几乎总是使用 make_shared 创建一个对象由 shared_ptrs 拥有?.
Note that this is the recommended default way to create shared_ptr
s with managed objects. See Why should you almost always use make_shared to create an object to be owned by shared_ptrs?.
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