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Random C++ Concepts

Container Adapters and Important C++ Concepts

Container Adapter

A container adapter is a wrapper around an existing container (like vector, deque, etc.) that provides a restricted interface—specialized for a particular usage pattern.

They adapt underlying containers to provide specific functionality like a stack, queue, or priority queue.

For example, a stack adapter uses a vector or deque to provide LIFO (Last In First Out) access, while a queue adapter uses a deque to provide FIFO (First In First Out) access. This allows you to use the underlying container's features while enforcing a specific access pattern.

📦 Types of Container Adapters

Adapter Behavior Default Underlying Container
stack LIFO (Last-In-First-Out) deque
queue FIFO (First-In-First-Out) deque
priority_queue Highest priority first vector (with make_heap)

🔍 binary_search in C++ (STL)

The binary_search function in C++ (from <algorithm>) checks whether a given element exists in a sorted range.

Syntax

bool binary_search(start_iterator, end_iterator, value);
// end_iterator: Iterator pointing past the end of the range.

↻ Rotate Example

rotate(arr, arr + 3, arr + 5);

This rotates the range [arr, arr+5) around the point arr + 3.

Vector Resize

vec.resize(new_size);                 // Resize to new_size elements
vec.resize(new_size, default_value);  // Fill new elements with default_value
  • default_value is the value to fill the new elements with.
  • end_iterator (e.g., v.end()) points just past the last element.

🖋️ String Append

string str = "Hello";
str.append(" World"); // Appends " World" to str
str += " World";      // Another way to append " World" to str

Use insert to insert a substring at a specific position in the string.

📊 Overloading Issue

double add(int = 0, double d = 0.0);
int add(int = 0, double d = 0.0);

These two overloads are NOT allowed because they only differ in return type.

🛠️ operator new(size_t size)

  • Allocates raw memory (like malloc in C).
  • Does not call any constructor.
  • Returns a void* pointer.
  • Defined in <new>.

🔢 Static Functions

Static functions can be accessed via objects too, although it's not recommended.

🏰 Constructor and Destructor Call Order

When an object of class C is instantiated:

  • Constructor of B is called,
  • Which calls constructor of A, printing A then B.
  • Data members of C are created, again printing A then B.
  • Finally, constructor of C is executed.

Destruction happens in reverse order after main() ends.

🤔 Most Vexing Parse

Number n1();
  • Looks like it's creating an object, but it's not!
  • It declares a function named n1 returning Number.

Why?

  • C++ prefers function declaration if it can be interpreted that way.

Correct ways to create an object:

Number n1;   // Direct
Number n1{}; // Uniform initialization

📂 Initialization List Order

MyClass(const char* _s1, const char* _s2, const char* _s3)_*_*_*