Dynamic Memory Allocation in Programming

Process Overview

• A process is an executing program, central to computational functions on a computer.
• Operates as a unit of work managed by the operating system.
• The program counter and processor registers reflect the process's current activity.

Memory Layout of a Process

• Memory organization for processes includes several segments:
  • Text Segment: Stores the program's machine code instructions.
  • Stack: Contains local variables, function parameters, and return addresses.
  • Data Section: Holds global variables (initialized and uninitialized).
  • Heap: Used for memory dynamically allocated at runtime.

Function Calls and Memory Management

• When a function is called, a stack frame is allocated for local variables and arguments.
• Upon function return, the stack frame is deallocated, and the stack pointer repositions upward.
• Memory allocation can occur dynamically using the malloc() function, and it should be freed with free() after use.

Global and Local Variables

• Global variables exist throughout the program's execution and are stored in the data section.
• Local variables are confined to the scope of functions and stored in the stack segment.

Dynamic Memory Allocation

• Dynamic memory is allocated during runtime, essential for creating complex data structures.
• The heap grows toward higher memory addresses, allowing for flexible memory usage.

Example Code Insights

• Global variables can be initialized (stored in the data section) or uninitialized (in the BSS segment).
• In the example code, a global variable global_var is initialized to 10, while local_var inside the function is initialized to 20.
• Usage of dynamically allocated memory (malloc) demonstrates how the heap manages memory during program execution.

Loading and Executing Programs

• Programs transition from a passive state (stored on disk) to an active state when loaded into memory and executed as a process.
• Common execution methods include double-clicking the executable icon or using command-line input.
• Multiple processes can run the same program independently with separate resource allocations.

Operating System Principles

• Each process operates within its own virtual address space, isolating it from other processes to ensure stability and security.