Question

C++ help

Computer Architecture, Memory and Data Representation

(a) The basic layout of memory can be divided into four main areas. What arethey and what are they used for?

(b) Give a short description to explain each of the following statements, including any terms used.

i. We sometimes have to defragment the heap.

ii. Local variables within a function do not need to be explicitly deleted when you return from that function.

(c) What is the decimal number 126 in binary notation? Note: the most significant bit should be on the left-hand side. Show your working.

(d) What is the decimal value of the hexadecimal number 0xFE? Show your working

Answer 1

(a) The four main areas of basic layout of memory in a typical C++ program are as follows :-

1. Code Segment :-

The code segment (a.k.a text segment) is the part of memory that contains machine code of the compiled C++ program. Code segment is exactly what the CPU executes. This part of memory is shareable to avoid wastage of memory since some frequently executing applications such as text editors and web browsers need this repeatedly. Also, since the code for a text editor won't change (and shouldn't too, for proper functioning), this part is usually read-only.

2. Data segment :-

This part of memory contains the static and global variables.

It is of two types ;-

1. Initialized data segment :-

Contains variables that are initialized to some fixed value.

Example :

int a = 5; // a can be assigned a different value and a is initialized to 5

2. Uninitialized data segment (BSS segment) :-

Contains variables that aren't initialized by programmer. Variables in this segment are initialized by kernel to arithmetic 0.

Example :

long b , arr[100]; // b is not assigned any value and arr is an array of 100 integers that haven't been initialized

3. Stack Segment :-

This segment holds the function caller stack - every time a function is called information is saved onto the stack segment. This information includes the address to return to along with some registers. Other things that are stored on stack segment are automatic variables.

4. Heap :-

Heap is the part of memory where dynamic allocation of memory usually happens. Heap usually grows upwards whereas the stack grows downwards

Usually the stack and heap are adjacent because if we keep code or data segment in between them, chances are heap and stack will expand and overwrite them.

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