Symbian Programming Summary-Basic article-class type

Original: http://discussion.forum.nokia.com/forum/showthread.php?t=68969

Translated from developer Library»symbian OS guide»essential idioms»class types

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Applications on Symbian OS use 4 commonly used classes, which are:

A value class that begins with T, which does not own any external objects, but refers directly to or indirectly through a handle to an external object.

A heap-allocation class that starts with C, which is all derived from CBase.

A resource class that begins with R, and the R class object contains a handle to a resource in another location.

An interface class that begins with M that defines an interface but requires a derived class implementation.

These classes are related to the requirements of the Purge mechanism, please refer to the SDK (Developer Library»symbian OS guide»c++ API guide»base»memory management»using Cleanup S Upport»cleanup Stack basics»cleanup requirements).

Value type: T class

The most basic classes are value types, and their names begin with T.

The T class contains their values, but they do not own any external objects, but simply refer directly to them through the pointer or indirectly refer to an external object through a handle.

The T class can be allocated on the stack (c + + automatic variables), or it can be members of other classes.

The basic features of the T class are described below.

constructor function:

Many of the T classes are so simple that constructors are not needed at all, and those that contain constructors initialize member data through constructors.

Copy constructors and assignment operators:

Copy Constructors (TX (const tx&)) and assignment operators (tx& operator= (const tx&) are rarely needed because copies are shallow copies, and T classes are almost always copied by members. The C + + compiler produces the default copy constructor and assignment operator.

These two functions are required when the T class is a template class that has an integer parameter, in which case the copy or assignment tx<32> to the tx<40> is more complex than the bitwise copy, so the copy constructor and assignment operator need to be explicitly implemented.

destructor:

The T class does not require a destructor, because there is no external resource that needs to be purged when the T class life cycle ends.

Destroy

The T class can be safely destroyed on the stack, which means that the memory can be freed without the destructor. Because the T class does not own external resources, there is no access to external resources when the class T object is destroyed.

function arguments

As a function parameter, the T class can be passed by value and reference.

Data members

The T class can contain other T-class objects and, in addition, can contain pointers to R-class objects or C-class objects that are cleared by another class or function, and are rarely used in practice.

Standard class level: Class C and CBase

The classes that use the most are in addition to the T class and the C class, which derives directly or indirectly from the CBase class.