Shulou(Shulou.com)05/31 Report--

In this article, the editor introduces in detail "instance analysis of static member variables of C++ class" with detailed contents, clear steps and proper handling of details. I hope that this article "instance analysis of static member variables of C++ class" can help you solve your doubts.

I. Review of member variables

Public member variables can be accessed through object names

The member variables of each object are exclusive.

Member variables cannot be shared between objects

Second, new demand

Count the number of objects in a class during the run of the program

Ensure the security of the program (global variables cannot be used)

You can get the number of current objects at any time

Let's look at an example:

# include int gCount = 0; class Test {private: int mCount;public: Test (): mCount (0) {gCount++;} ~ Test () {--gCount;} int getCount () {return gCount;}}; Test gTest;int main () {Test T1; Test T2; printf ("count =% d\ n", gTest.getCount ()) Printf ("count =% d\ n", t1.getCount ()); printf ("count =% d\ n", t2.getCount ()); return 0;}

The output is as follows:

Although this code can get the number of currently defined objects, but the use of global variables can not guarantee the security of the program, so what is the good way? Look at the following.

Static member variables

Static member variables can be defined in C++

Static member variables belong to the entire class

The lifetime of static member variables does not depend on any object

You can access public static member variables directly through the class name

All objects share the static member variables of the class

You can access public static member variables through object names

Characteristics of static member variables

Directly modified by the static keyword when defining

Static member variables need to allocate space separately outside the class

Static member variables are located in the global data area within the program

Grammar rules:

Type ClassName:VarName = value

Let's look at the use of static member variables:

# include class Test {private: static int cCount;public: Test () {cCount++;} ~ Test () {--cCount;} int getCount () {return cCount;}}; int Test::cCount = 0TestTest gTest;int main () {Test T1; Test T2; printf ("count =% d\ n", gTest.getCount ()) Printf ("count =% d\ n", t1.getCount ()); printf ("count =% d\ n", t2.getCount ()); Test* pt = new Test (); printf ("count =% d\ n", pt- > getCount ()); delete pt; printf ("count =% d\ n", gTest.getCount ()); return 0;}

The output is as follows:

Test* pt = new Test (); A test object is dynamically generated in the heap space, so a call to the constructor is triggered, so count becomes 4 and delete pt; becomes 3.

After reading this, the article "instance Analysis of static member variables of C++ Class" has been introduced. If you want to master the knowledge of this article, you still need to practice and use it before you can understand it. If you want to know more about related articles, welcome to follow the industry information channel.

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