对于相同数据类型的数据，我们可以使用数组来表示，然而对于有不同数据类型的一组数据就不能使用数组，那用什么呢？所以有了结构体。结构体定义在栈中，或者作为对象的属性存在堆中。而对象存在于堆中。如果接触过c＋＋，C++中有两种对象，一种是栈对象，另一种是堆对象。C++中对象和结构体就非常相似了。

You can use both classes and structures to define custom data types to use as the building blocks of your program’s code.

However, structure instances are always passed by value , and class instances are always passed by reference . This means that they are suited to different kinds of tasks. As you consider the data constructs and functionality that you need for a project, decide whether each data construct should be defined as a class or as a structure.

As a general guideline, consider creating a structure when one or more of these conditions apply:

• The structure’s primary purpose is to encapsulate a few relatively simple data values.
• It is reasonable to expect that the encapsulated values will be copied rather than referenced when you assign or pass around an instance of that structure.
• Any properties stored by the structure are themselves value types, which would also be expected to be copied rather than referenced.
• The structure does not need to inherit properties or behavior from another existing type.

Examples of good candidates for structures include:

• The size of a geometric shape, perhaps encapsulating a width property and a height property, both of type Double .
• A way to refer to ranges within a series, perhaps encapsulating a start property and a length property, both of type Int .
• A point in a 3D coordinate system, perhaps encapsulating x , y and z properties, each of type Double .

In all other cases, define a class, and create instances of that class to be managed and passed by reference. In practice, this means that most custom data constructs should be classes, not structures.

结构体用来存储简单数据结构用的，比如坐标系的数据结构，几何图形的数据结构等。因为它的存在使你可以不用class去存储很low的数据结构，在使用时也会很简单粗暴的值传递，少了class的复杂性。

struct是值传递的，class是引用传递的。