Class Templates

Generic Data Structures

💡 Class template ek "universal container blueprint" hai — ek "Box" design karo jo kisi bhi cheez (int, string, koi bhi object) ko hold kar sake, bina har type ke liye alag Box class banaye.

Class templates function templates jaisa hi concept hai, lekin poori class ke liye — generic data structures banane ke liye bahut use hota hai (jaise apna khud ka Stack, Container). C++ ki poori STL (Standard Template Library) isi concept par based hai — vector<int>, vector<string> sab ek hi generic vector template ke instances hain.

Object banate waqt actual type specify karna padta hai angle brackets mein: Box<int> ya Box<string> — compiler us specific type ke liye class generate kar deta hai.

template <typename T>
class Box {
  private:
    T value;
  public:
    Box(T v) : value(v) {}
    T getValue() { return value; }
};

int main() {
  Box<int> intBox(42);
  Box<string> strBox("Hello");

  cout << intBox.getValue() << endl;   // 42
  cout << strBox.getValue() << endl;   // Hello
  return 0;
}

📦

Class template ek "universal container blueprint" hai — ek "Box" design karo jo kisi bhi cheez (int, string, koi bhi object) ko hold kar sake, bina har type ke liye alag Box class banaye.

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⚡ झट से Recap

Class template = generic class, kisi bhi type ke saath instantiate ho sakti hai
Box<Type> syntax se specific type specify karo
Puri STL (vector, map, etc.) class templates par based hai

इस page में (2 subtopics)

Class templates mein default type specify kar sakte ho — agar user type na de, ek default use ho jaata hai. Ye STL containers mein bhi common hai (jaise vector ka allocator template parameter default hota hai).

template <typename T = int>
class Container {
  T value;
  public:
    Container(T v) : value(v) {}
    T get() { return value; }
};

int main() {
  Container<> c1(10);         // default T=int use hota hai
  Container<double> c2(3.14); // explicit double

  cout << c1.get() << endl;   // 10
  cout << c2.get() << endl;   // 3.14
  return 0;
}

💡Tip: Container<> mein khaali angle brackets zaroori hain (default type use karne ke liye bhi) — sirf Container c1(10); likhna valid nahi hai class templates ke liye.

Template parameters sirf types hi nahi ho sakte — actual VALUES (jaise int) bhi ho sakte hain. Ye compile-time constants ke liye useful hai, jaise fixed-size arrays ki size template parameter se specify karna.

template <typename T, int Size>
class FixedArray {
  T data[Size];
  public:
    int getSize() { return Size; }
};

int main() {
  FixedArray<int, 5> arr;   // Size = 5, compile-time constant
  cout << arr.getSize() << endl;  // 5
  return 0;
}

💡Tip: std::array<T, N> (STL) isi pattern ka real-world example hai — N ek non-type template parameter hai jo array ki fixed size compile-time par decide karta hai.

← पिछला🧵 Function Templates अगला →📊 vector — Dynamic Array

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Class Templates

Template with Default Type

Non-Type Template Parameters