Teaching Notes: Module 06

Key Learning Objectives

• Four C++ cast types
• When to use each cast
• Type detection at runtime
• Serialization concepts

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Exercise 00: Scalar Type Converter

Type Detection Order

1. Check for char (single printable char)
2. Check for int (all digits, optional sign)
3. Check for float (has ‘f’ suffix)
4. Check for double (decimal point, no ‘f’)
5. Handle special: nan, inf, nanf, inff

Common Mistakes

1. Not handling all edge cases

   • Empty string
   • Just ”-” or ”+”
   • Multiple decimal points
   • “nan” vs “nanf”

2. Display format issues

   // Float/double should show .0 for whole numbers
   std::cout << std::fixed << std::setprecision(1);
   std::cout << 42.0f;  // "42.0f" not "42f"

3. Overflow detection

   • int overflow -> “impossible”
   • Non-displayable char -> “Non displayable”

Which Cast?

• Numeric conversions: static_cast

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Exercise 01: Serialization

Key Concept

Convert pointer to integer and back.

uintptr_t Serializer::serialize(Data* ptr) {
    return reinterpret_cast<uintptr_t>(ptr);
}

Data* Serializer::deserialize(uintptr_t raw) {
    return reinterpret_cast<Data*>(raw);
}

Which Cast?

• reinterpret_cast - bit-level reinterpretation

Common Mistakes

1. Empty Data struct

   • Subject requires non-empty Data

2. Not testing round-trip

   Data d;
   uintptr_t raw = Serializer::serialize(&d);
   Data* result = Serializer::deserialize(raw);
   assert(result == &d);  // Must be same address!

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Exercise 02: Type Identification

Without typeinfo

Must use dynamic_cast to identify types.

Pointer Version (returns NULL on failure)

void identify(Base* p) {
    if (dynamic_cast<A*>(p))
        std::cout << "A" << std::endl;
    else if (dynamic_cast<B*>(p))
        std::cout << "B" << std::endl;
    else if (dynamic_cast<C*>(p))
        std::cout << "C" << std::endl;
}

Reference Version (throws on failure)

void identify(Base& p) {
    try {
        (void)dynamic_cast<A&>(p);
        std::cout << "A" << std::endl;
        return;
    } catch (...) {}
    // Try B, C...
}

Common Mistakes

1. Using typeid (forbidden)

   • <typeinfo> header is forbidden

2. Pointer inside reference version

   • Subject forbids using pointer in reference version

3. Base must be polymorphic

   • Need at least one virtual function (virtual destructor counts)

Which Cast?

• dynamic_cast - runtime type identification