Storage Class in C++

Types of Storage Classes

In C++ there are four commonly discussed storage classes:

1. Auto Storage Class
   • This is the default storage class for variables declared inside a function or a block.
   • Writing the auto keyword explicitly is rarely needed for ordinary local variables (it has different modern uses in C++11+ for type deduction).
2. Extern Storage Class
   • extern indicates that a variable or function has external linkage, typically defined in another translation unit.
   • It is used to access a global variable from other source files.
3. Register Storage Class
   • register suggests to the compiler that the variable be stored in a CPU register for faster access.
   • Modern compilers usually ignore this hint; the optimizer makes register allocation decisions.
4. Static Storage Class
   • static variables preserve their value between function calls and exist for the entire program lifetime.
   • static at namespace/global scope makes the symbol have internal linkage (visible only within that translation unit).