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Storage Classes

Storage Classes. Storage Classes. Storage class tells : 1) Where the variable is stored. 2) Initial value of the variable. 3) Scope of the variable. (which a variable is accessed.) 4) Life of the variable. Storage Classes. There are four types of storage classes:

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Storage Classes

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  1. Storage Classes

  2. Storage Classes • Storage class tells : • 1) Where the variable is stored. • 2) Initial value of the variable. • 3) Scope of the variable. (which a variable is accessed.) • 4) Life of the variable.

  3. Storage Classes • There are four types of storage classes: • 1) Automatic storage class • 2) Register storage class • 3) Static storage class • 4) External storage class

  4. Storage Classes • Automatic storage class • Variable is stored in memory. • Default value is garbage value • Scope is local to the block where it is declared • Life is, with in the block in where it is declared • Automatic variable can be declared using the keyword auto • Eg: auto int a; • By default all variables are automatic • int a; same as auto int a;

  5. Storage Classes • Example 1: • main() • { • auto inti=10; • printf(“%d”,i); • } • Output: • 10 • Example 2: • main() • { • auto inti; • printf(“%d”,i); • } • Output: • 1002 • In example 1, i value is initialised to 10.So,output is 10. • In example 2, i value is not initialized. So,compiler reads i value is a garbage value.

  6. Storage Classes • Register storage class • Variable is stored in a register instead of RAM. • Default value is garbage value • Scope is local to the block where it is declared • Life is, with in the block in where it is declared

  7. Storage Classes • Register storage class • When a variable stored in register, it access high speed • The no of registers are limited in a processor, if the registers are not free it will convert to automatic variable • The mostly length of the registers are 2 bytes, so we cannot store a value greater than its size, if it so it will covert to automatic variable • Register variable can be declared using the keyword register • Eg: register int a;

  8. Storage Classes Static - Storage Class • Variable is stored in memory. • Default value is 0 • Scope local to the block. • Life is, value of the variable persists between different function calls. • static variable can be declared using the keyword static • Eg: static int a;

  9. Storage Classes Static - Storage Class • static can also be defined within a function. • The variable cannot reinitialized when the function is called. • This inside a function static variable retains its value during various calls. • main() • { void show(); show(); show(); • } • void show() { • static int a=10; • printf(“%d”,a); • a++; • } • o/p will be 10 11 • second time a=10; will not execute

  10. Storage Classes • External - Storage Class • Variable is stored in memory. • Default value is 0 • Scope is end of the program • Life is, with in the block in end of the program • external variable can be declared using the keyword extern • extern is used to give a reference of a global variable that is visible to ALL the program files.

  11. Storage Classes • External - Storage Class • extern int a=10; • void main() • { • vid show(); printf(“a= %d”,a); show(); • } • void show() • { • printf(“%d”,a); • } • Output a=10 10

  12. Storage Classes • External - Storage Class • The extern keyword is used before a variable to inform the compiler that the variable is declared some where else.

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