Storage Classes in C

The role of storage classes in computer programming

• Control over the scope and lifetime of identifiers
• Efficient memory management and resource utilisation
• Minimisation of errors during program execution
• Improved code reusability and organisation

Exploring Different Types of Storage Classes in C

• Storage: Memory (RAM)
• Lifetime: Within the block/function where it is declared
• Initial Value: Garbage value (uninitialised)
• Scope: Local

#include 

void function() {
  auto int x = 1; // x is an auto variable
  printf("Value of x: %d\n", x);
  x++;
  printf("Value of x after increment: %d\n", x);
}

int main() {
  function();
  function();
  return 0;
}

Extern Storage Class in C: use and implications

• Storage: Memory (RAM)
• Lifetime: Throughout program execution
• Initial Value: Depends on where the variable or function is defined
• Scope: Global

#include 
#include "function.h"

int x; // value of the global variable x is shared across files

int main() {
  x = 5;
  printf("Value of x before increment: %d\n", x);
  increment();
  printf("Value of x after increment: %d\n", x);
  
  return 0;
}

#ifndef FUNCTION_H
#define FUNCTION_H

void increment(void);

#endif

#include "function.h"

extern int x; // tells the compiler that x is defined in another file

void increment() {
  x++;
}

In this example, both 'main.c' and 'function.c' share the global variable 'x', and its value is incremented using the 'increment()' function defined in 'function.c'. By using the 'extern' storage class, we can share the global variable 'x' between different program files and avoid redeclaring it.

Register Storage Class in C: benefits and limitations

• Storage: CPU Registers
• Lifetime: Within the block/function where it is declared
• Initial Value: Garbage value (uninitialised)
• Scope: Local

#include 

int main() {
  register int i; // i is declared as a register variable
  
  for (i = 0; i < 1000000; i++) {
    // A time-sensitive operation or calculation
  }
  
  return 0;
}

Static Storage Class in C: distinguishing it from other classes

• Storage: Memory (RAM)
• Lifetime: Throughout program execution
• Initial Value: Zero (0) for variables; functions remain in memory
• Scope: Local (variables) and global (functions)

#include 

void function() {
  static int x = 0; // x is declared as a static variable
  x++;
  printf("Value of x: %d\n", x);
}

int main() {
  function(); // x is 1
  function(); // x is 2
  return 0;
}

Storage Class Specifiers in C: A Comprehensive Look

auto data_type variable_name;

register data_type variable_name;

static data_type variable_name; // For variables

static return_type function_name(parameters); // For functions

extern data_type variable_name; // For variables

extern return_type function_name(parameters); // For functions

• Using `register` storage class for variables involved in time-critical operations or calculations to speed up the performance
• Applying the `static` storage class for local variables to persist their values between function calls
• Utilising the `extern` storage class specifier to access global variables or functions shared across different files in a project