[英]Initialise C-structs in C++
I am creating a bunch of C structs so i can encapsulate data to be passed over a dll c interface. 我正在创建一堆C结构,所以我可以封装要通过dll c接口传递的数据。 The structs have many members, and I want them to have defaults, so that they can be created with only a few members specified.
结构体有很多成员,我希望它们具有默认值,这样它们只需指定几个成员即可创建。
As I understand it, the structs need to remain c-style, so can't contain constructors. 据我了解,结构需要保持c风格,因此不能包含构造函数。 Whats the best way to create them?
什么是创建它们的最佳方式? I was thinking a factory?
我在想一家工厂?
struct Foo {
static Foo make_default ();
};
A factory is overkill. 一家工厂太过分了。 You use it when you want to create instances of a given interface, but the runtime type of the implementation isn't statically known at the site of creation.
您希望创建给定接口的实例时使用它,但在创建的站点上不能静态地知道实现的运行时类型。
The C-Structs can still have member functions. C-Structs仍然可以具有成员函数。 Problems will, however, arise if you start using virtual functions as this necessitates a virtual table somewhere in the struct's memory.
但是,如果您开始使用虚函数,则会出现问题,因为这需要在结构内存中的某个位置使用虚拟表。 Normal member functions (such as a constructor) don't actually add any size to the struct.
普通成员函数(例如构造函数)实际上不向结构添加任何大小。 You can then pass the struct to the DLL with no problems.
然后,您可以毫无问题地将结构传递给DLL。
I would use a constructor class: 我会使用构造函数类:
struct Foo { ... };
class MakeFoo
{
Foo x;
public:
MakeFoo(<Required-Members>)
{
<Initalize Required Members in x>
<Initalize Members with default values in x>
}
MakeFoo& optionalMember1(T v)
{
x.optionalMember1 = v;
}
// .. for the rest option members;
operator Foo() const
{
return x;
}
};
This allows to arbitrary set members of the struct in expression: 这允许在表达式中任意设置结构的成员:
processFoo(MakeFoo(1,2,3).optionalMember3(5));
I have an easy idea, here is how: 我有一个简单的想法,这是如何:
Make the structure, just like you normally would, and create a simple function that initializes it: 像通常那样制作结构,并创建一个初始化它的简单函数:
struct Foo{...};
void Default(Foo &obj) {
// ... do the initialization here
}
If you have multiple structures, you are allowed in C++ to overload the function, so you can have many functions called 'default', each initializing its own type, for example: 如果你有多个结构,你可以在C ++中重载函数,所以你可以有许多名为'default'的函数,每个函数都初始化它自己的类型,例如:
struct Foo { //... };
struct Bar { //... };
void Default(Foo &obj) {...}
void Default(Bar &obj) {...}
The C++ compiler will know when to call the first or the second overload based on the parameter. C ++编译器将根据参数知道何时调用第一个或第二个重载。 The & makes obj a reference to whatever parameter you give it, so any changes made to obj will be reflected to the variable you put as parameter.
&使obj引用您给出的任何参数,因此对obj所做的任何更改都将反映到您作为参数放置的变量中。
Edit: I also have an idea for how to specify some parameters, you can do it by using default parameters. 编辑:我也知道如何指定一些参数,你可以使用默认参数。 This is how it works:
这是它的工作原理:
For example you the following function; 例如,你有以下功能; you can specify default values for parameters like this:
您可以为这样的参数指定默认值:
void Default (Foo &obj, int number_of_something = 0, int some_other_param = 10)
{ ... }
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