![DATA SEGMENT
• Initialized data segment: An initialized data segment is also known as
the data segment. A data segment is a virtual address space of a program
that contains all the global and static variables which are explicitly
initialized by the programmer.
char string[] = "javatpoint"; // global variable stored in initiali
zed data segment in read-write area..
int main()
{
static int i = 90; // static variable stored in initialized data seg
ment..
return 0;
}](https://image.slidesharecdn.com/cmemorymodel-220825095023-c9b9589c/85/C-MEMORY-MODEL-pptx-10-320.jpg)
C MEMORY MODEL.pptx
- 2. MEMORY MODEL • Defines the semantics of computer memory storage for the purpose of the C abstract machine. • The data storage (memory) available to a C program is one or more contiguous sequences of bytes. • Each byte in memory has a unique address. • Pointers present us with a certain abstraction of the environment and state in which our program is executed, the C memory model.
- 4. SECTIONS OF MEMORY • A typical memory representation of a C program consists of the following sections. 1. Text segment (i.e. instructions) 2. Initialized data segment 3. Uninitialized data segment (bss) 4. Heap 5. Stack
- 6. TEXT SEGMENT • A text segment, also known as a code segment or simply as text, is one of the sections of a program in an object file or in memory, which contains executable instructions. • As a memory region, a text segment may be placed below the heap or stack in order to prevent heaps and stack overflows from overwriting it. • Usually, the text segment is sharable so that only a single copy needs to be in memory for frequently executed programs, such as text editors, the C compiler, the shells, and so on.
- 7. DATA SEGMENT • The data which we use in our program will be stored in the data section. • Since the variables declared inside the main() function are stored in the stack, but the variables declared outside the main() method will be stored in the data section. • The variables declared in the data section could be stored in the form of initialized, uninitialized, and it could be local or global. • Therefore, the data section is divided into four categories, i.e., initialized, uninitialized, global, or local.
- 8. EXAMPLE int var1; int var2 = 10; void function1() { printf("I am function1"); } int main() { function1(); return 0; } • Here, var1 and var2 variables are declared outside the main() function where var1 is the uninitialized variable, whereas the var2 is an initialized variable. • These variables can be accessed anywhere in the program because these variables are not a part of the main() in the stack.
- 9. DATA SEGMENT • The data segment consists of two segments: 1. Uninitialized data segment: The uninitialized data segment is also known as a .bss segment that stores all the uninitialized global, local and external variables. The .bss segment stands for Block Started by symbol. char a; // uninitialized global variable.. int main() { static int a; // uninitialized static variable.. return 0; }
- 10. DATA SEGMENT • Initialized data segment: An initialized data segment is also known as the data segment. A data segment is a virtual address space of a program that contains all the global and static variables which are explicitly initialized by the programmer. char string[] = "javatpoint"; // global variable stored in initiali zed data segment in read-write area.. int main() { static int i = 90; // static variable stored in initialized data seg ment.. return 0; }
- 11. STACK • The stack area traditionally adjoined the heap area and grew in the opposite direction; when the stack pointer met the heap pointer, free memory was exhausted. • When we define a function and call that function then we use the stack frame. • The stack section plays a very important role in the memory because whenever the function is called, a new stack frame is created. • Stack is also used for recursive functions.
- 12. HEAP • Heap memory is used for the dynamic memory allocation. Heap memory begins from the end of the uninitialized data segment and grows upwards to the higher addresses. • The malloc() and calloc() functions are used to allocate the memory in the heap. • The heap memory can be used by all the shared libraries and dynamically loaded modules. • The free() function is used to deallocate the memory from the heap.
- 13. EXAMPLE #include<stdio.h> int main() { int *ptr = (int*)malloc(sizeof(int)) ; // memory gets allocated i n the heap segment. return 0; }