Storage classes in c++

Storage Classes
in C++
Presented by : Jaspal Singh

What are Storage Classes
in C++ Programming ?

Types of Storage Classes
 Automatic
 External
 Static
 Register
 Mutable

Storage Class Keyword Lifetime Visibilty
Automatic auto Function Block Local
External extern Whole Program Global
Static static Whole Program Local
Register register Function Block Local
Mutable Mutable Class Local

Automatic Storage Class
Syntax of Automatic Storage :
datatype var_name1 [= value];
Or
auto datatype var_name1 [= value];
Example of Automatic Storage Class :
auto int x;
float y = 5.67;

External Storage Class
Syntax of External Storage Class :
extern datatype var_name1;
For example:
extern float var1;

Example of External Storage Class
File: sub.cpp
int test=100; // assigning value to test
void multiply(int n)
{
test=test*n;
}
File: main.cpp
#include<iostream>
#include "sub.cpp" // includes the content of sub.cpp
using namespace std;
extern int test; // declaring test
int main()
{
cout<<test<<endl;
multiply(5);
cout<<test<<endl;
return 0;
}
Output
100
500

Static Storage Class
Syntax of Static Storage Class
static datatype var_name1 [= value];
For example
static int x = 101;
static float sum;

Register Storage Class
Syntax of Register Storage Class
register datatype var_name1 [= value];
For example
register int id;
register char a;

Example : C++ program to create automatic,
static and register variables.
#include<iostream>
int g; //global variable, initially holds 0
void test_function()
{
static int s; //static variable, initially
holds 0
register int r; //register variable
r=5;
s=s+r*2;
cout<<"Inside test_function"<<endl;
cout<<"g = "<<g<<endl;
cout<<"s = "<<s<<endl;
cout<<"r = "<<r<<endl;
}
int main()
{
int a; //automatic variable
g=25;
a=17;
test_function();
cout<<"Inside main"<<endl;
cout<<"a = "<<a<<endl;
cout<<"g = "<<g<<endl;
test_function();
return 0;
}

Output
Output
Inside test_function
g = 25
s = 10
r = 5
Inside main
a = 17
g = 25
Inside test_function
g = 25
s = 20
r = 5

Mutable Storage Class
Syntax for Mutable Storage Class Declaration
mutable datatype var_name1;
For example
mutable int x;
mutable char y;

Example of Mutable Storage Class
#include<iostream>
class test
{
mutable int a;
int b;
public:
test(int x,int y)
{
a=x;
b=y;
}
void square_a() const
{
a=a*a;
}
void display() const
{
cout<<"a = "<<a<<endl;
cout<<"b = "<<b<<endl;
}
};
int main()
{
const test x(2,3);
cout<<"Initial value"<<endl;
x.display();
x.square_a();
cout<<"Final value"<<endl;
x.display();
return 0;
}

Output
Output
Initial value
a = 2
b = 3
Final value
a = 4
b = 3

Storage classes in c++

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