storage class

 


Storage Classes are used to describe the features of a variable/function. These features basically include the scope, visibility and life-time which help us to trace the existence of a particular variable during the runtime of a program. 


C++ uses 5 storage classes, namely:




auto

register

extern

static

mutable



1. auto:                                                  

=========

The auto keyword provides type inference capabilities, using which automatic deduction of the data type of an expression in a programming language can be done.


It is the default storage class for all local variables. The auto keyword is applied to all local variables automatically.


{   

auto int y;  

float y = 3.45;  

}  

The above example defines two variables with a same storage class, auto can only be used within functions.






2.register:

==========

 This storage class declares register variables which have the same functionality as that of the auto variables.

 The only difference is that the compiler tries to store these variables in the register of the microprocessor 

 if a free register is available. This makes the use of register variables to be much faster than that of the variables stored in the memory during the runtime of the program. If a free register is not available, 

 these are then stored in the memory only.

 Usually, a few variables which are to be accessed very frequently in a program are declared with the register keyword which improves the running time of the program

 

 The register variable allocates memory in register than RAM. Its size is same of register size. It has a faster access than other variables.


It is recommended to use register variable only for quick access such as in counter.


Note: We can't get the address of register variable.


register int counter=0;    




3. Extern storage class


 simply tells us that the variable is defined elsewhere and not within the same block where it is used.

 Basically, the value is assigned to it in a different block and this can be overwritten/changed in a different block as well. 


External Storage Class

The extern variable is visible to all the programs. It is used if two or more files are sharing same variable or function.


=========

#include <iostream>

using namespace std;


// declaring the variable which is to

// be made extern an intial value can

// also be initialized to x

int x;

void externStorageClass()

{


cout << "Demonstrating extern class\n";


// telling the compiler that the variable

// x is an extern variable and has been

// defined elsewhere (above the main

// function)

extern int x;


// printing the extern variables 'x'

cout << "Value of the variable 'x'"

<< "declared, as extern: " << x << "\n";


// value of extern variable x modified

x = 2;


// printing the modified values of

// extern variables 'x'

cout

<< "Modified value of the variable 'x'"

<< " declared as extern: \n"

<< x;

}


int main()

{


// To demonstrate extern Storage Class

externStorageClass();


return 0;

}  0,2 0utput

====================================


extern int counter=0;   

=========================

4.static:

=======

 This storage class is used to declare static variables which are popularly used while writing programs in C++ language. 


Static variables have a property of preserving their value even after they are out of their scope! 


qaHence, static variables preserve the value of their last use in their scope.




==================================

The static variable is initialized only once and exists till the end of a program. It retains its value between multiple functions call.


The static variable has the default value 0 which is provided by compiler.


#include <iostream>  

using namespace std;  

void func() {    

   static int i=0; //static variable    

   int j=0; //local variable    

   i++;    

   j++;    

   cout<<"i=" << i<<" and j=" <<j<<endl;    

}    

int main()  

{  

 func();    

 func();    

 func();    

}  

Output:


i= 1 and j= 1

i= 2 and j= 1

i= 3 and j= 1

===================================












5.mutable: Sometimes there is a requirement to modify one or more data members of class/struct through const function even though you don’t want the function to update other members of class/struct. 

This task can be easily performed by using the mutable keyword. The keyword mutable is mainly used to allow a particular data member of const object to be modified. 

Comments

Post a Comment

Popular posts from this blog

Difference between Structure and Array in C

  On the basis of internal implementation following are some basic differences between both. Sr. No. Key Structure Array 1 Definition Structure can be defined as a data structure used as container which can hold variables of different types. On other hand Array is a type of data structure used as container which can hold variables of same type and do not support multiple data type variables. 2 Memory Allocation Memory allocation for input data in structure does not necessary to be in consecutive memory location. While in case of array the input data stored in contiguous memory allocation which implies that array stores data in such memory model where it assigns consecutive memory blocks (that is, memory blocks having consecutive addresses). 3 Accessibility In order to access the element in Structure we require to have the name of that element i.e it is mandatory to have element name for its retrieval from Structure. On other hand in case of Array we can access the element by index....
Read more

Mutitreading Notes

 https://www.bogotobogo.com/cplusplus/C11/1_C11_creating_thread.php Processes are independent while thread is within a process.   Processes have separate address spaces while threads share their address spaces. Processes communicate each other through inter-process communication. Processes carry considerable state (e.g., ready, running, waiting, or stopped) information, whereas multiple threads within a process share state as well as memory and other resources. Context switching  between threads in the same process is typically faster than context switching between processes. Multithreading  has some advantages over  multiple processes . Threads require less overhead to manage than processes, and intraprocess thread communication is less expensive than interprocess communication. Multiple process  concurrent programs do have one advantage: Each process can execute on a different machine ( distribute program ). Examples of distributed programs are file serve...
Read more