What is Memory Layout in C ?

In C, the memory layout refers to how the memory of a program is organized and divided into different sections to store various types of data and code during its execution. Understanding the memory layout is crucial for programmers because it helps them manage and manipulate memory effectively. In C, the memory layout typically consists of the following major sections:

1. Text Segment (Code Segment):
   • The text segment, also known as the code segment, is where the program’s executable code is stored.
   • It contains the machine code instructions that are executed by the CPU.
   • This segment is typically read-only to prevent accidental modification of the program’s instructions.
2. Data Segment:
   • The data segment contains two sub-sections:
     • Initialized Data: This sub-section stores global and static variables that have an initial value specified by the programmer. These variables are allocated at compile time.
     • Uninitialized Data (BSS – Block Started by Symbol): This sub-section stores global and static variables that are initialized to zero or have no initial value specified by the programmer. The memory for these variables is allocated but not initialized, so they are typically set to zero during program startup.
3. Heap:
   • The heap is a dynamically allocated memory area that is used for storing data that needs to persist beyond the scope of individual function calls.
   • Memory in the heap is managed explicitly by the programmer using functions like malloc() and free().
   • It is often used for dynamic data structures like linked lists, trees, and objects created at runtime.
4. Stack:
   • The stack is used to store local variables, function parameters, and control information for function calls.
   • It operates in a last-in-first-out (LIFO) manner, meaning that the most recently called function’s data is at the top of the stack.
   • The stack is managed automatically by the C runtime, and memory is allocated and deallocated as functions are called and return.
   • Stack memory is typically limited in size and meant for short-lived data.
5. Environment Variables and Command Line Arguments:
   • This section stores environment variables and command-line arguments that are passed to the program.
   • These values can be accessed using functions like getenv() and are typically used for configuration or customization of the program’s behavior.
6. Memory-Mapped Files (Optional):
   • On some systems, there may be a section for memory-mapped files, which allows the program to treat a file as if it were an array in memory.
   • This is an advanced feature and may not be present or used in all C programs.

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