storage classes in C - Computer science fundamentals tutorial

Storage class in C

Storage class defines the scope (visibility) and lifetime of variables and/or functions declared within a C program.  It stored in RAM or CPU register. There are Four storage class into which variables are declared & stored.

1.   Auto storage class.

2.   Static storage class.

3.   Extern storage class.

4.   Register storage class.

1.   Auto storage class: - Variable declared in this class is stored In RAM. This is the default storage class and the keyword ‘auto’ is used declare variables. Auto variables are active in a block in which they are declare. Auto storage class is commonly used in all C program without a keyword ‘auto’.

Example:- auto int a;

2.   Static storage class:- Variables declares in this class are also stored in the RAM. The keyword ‘static’ is used to declare these variables. Similar to auto variable, the static variable are also active in the block which they are declared and they retain the latest value.

Example: static int a=10;

3.   Extern storage class: - Global variable are decided using this class & they are stored in RAM. The key ‘extern’ is used to declare this variable. The global variables are also declared outside the main function. Extern class can be used consider a local variable in a block as a global variable.

Example: - extern int a;

4.   Register storage class: - Variables declare using this class is stored in the CPU memory register. The keyword register is used to declare these variables. Only a few variables which are frequently used in the program and declared using this class to improve the program executing speed. The behaviour of register variable is similar to that of auto variables except that their storage locations are different. In case of non availability of CPU memory register, these variables are stored in RAM as auto variables.

Example: - register int a;