Memory Layout in C

Memory layout in C refers to the organization of memory segments or regions used by a C program during its execution. Understanding the memory layout is crucial for writing efficient and safe C programs. The memory layout can vary slightly depending on the system and compiler, but the basic structure includes the following segments:

Text Segment (Code Segment):

• The text segment contains the executable code of the program.
• It is typically marked as read-only, meaning that you cannot modify the code while the program is running.
• The machine code instructions of your program reside in this segment.
• Also known as the “code segment” because it contains the program’s instructions.

Data Segment:

• The data segment is further divided into two parts:
  • Initialized Data Segment (or Data Section):
  • This part of the data segment contains global and static variables that are explicitly initialized with values.
  • Initialized variables are stored in a dedicated region of memory with their initial values.
  • Uninitialized Data Segment (BSS – Block Started by Symbol):
  • The BSS segment contains global and static variables that are uninitialized or explicitly initialized to zero.
  • These variables are allocated space in memory but not initialized to specific values.

Heap:

• The heap is a dynamically allocated region of memory used for storing data that can be allocated and deallocated at runtime.
• Memory allocated on the heap is managed by functions like malloc, calloc, realloc, and freed using free.
• The heap is used for dynamic data structures like linked lists, trees, and other data that must persist across function calls.

Stack:

• The stack is a region of memory used for function call management and local variables.
• Each function call in C typically creates a new stack frame, which includes the function’s parameters, return address, and local variables.
• The stack follows a last-in, first-out (LIFO) order, meaning that the most recently called function is at the top of the stack.
• As functions return, their stack frames are removed (popped) from the stack.

Environment Variables (Environment Variables Segment):

• This segment stores environment variables that can be accessed by the program.
• Environment variables are key-value pairs that can affect program behavior.
• You can access environment variables using functions like getenv in C.

Command Line Arguments (Command Line Arguments Segment):

• This segment stores command-line arguments passed to the program when it’s executed.
• Command-line arguments can be accessed through the main function’s argument list (argc and argv).

Understanding these memory segments and managing memory properly is essential for writing efficient and reliable C programs. Incorrect memory access or management can lead to bugs, crashes, or security vulnerabilities.