Forthcoming

scopes.cpp

/**
 * @file scopes.cpp
 * @author Jeffrey Bergamini for CS 19 Boot Camp, jeffrey.bergamini@cabrillo.edu
 *
 * Let's see how much you understand/remember about scope and lifetime in C++!
 */
 
#include <iostream>
 
int x;
 
void f1() {
  x = 2;
  std::cout << x << '\n';
}
 
void f2(int x) {
  std::cout << x << '\n';
  {
    int x;
    x = 4;
    std::cout << x << '\n';
  }
  x = 5;
  std::cout << x << '\n';
}
 
int main() {
  x = 1;
  std::cout << x << '\n';
  f1();
  std::cout << x << '\n';
  f2(3);
  std::cout << x << '\n';
  int x;
  x = 6;
  std::cout << x << '\n';
}

scopes_annotated.cpp

/**
 * @file scopes_annotated.cpp
 * @author Jeffrey Bergamini for CS 19 Boot Camp, jeffrey.bergamini@cabrillo.edu
 *
 * Let's add *memory addresses* to the output to see which symbol `x` represents in which context.
 */
 
#include <iostream>
 
int x;  // global variable, global scope
 
void f1() {
  x = 2;  // assigns to global variable `x`
  std::cout << &x << '\t' << x << '\n';
}
 
void f2(int x) {
  std::cout << &x << '\t' << x << '\n';
  {
    int x;  // local variable (local to function `f1()`), scoped within anonymous block
    x = 4;  // assigns to local variable `x` scoped within anonymous block
    std::cout << &x << '\t' << x << '\n';
  }
  x = 5;  // assigns to local variable `x` (function parameter)
  std::cout << &x << '\t' << x << '\n';
}
 
int main() {
  x = 1;  // assigns to global variable (i.e., global var `x` is a *lvalue*)
  std::cout << &x << '\t' << x << '\n';
  f1();
  std::cout << &x << '\t' << x << '\n';  // function `f1()` should have mutated global variable `x`
  f2(3);
  std::cout << &x << '\t' << x << '\n';  // function `f2()` has not mutated global variable `x`
  int x;                                 // local variable, local scope
  x = 6;  // assigns to local variable `x` (global `x` is now "shadowed" for the rest of the block)
  std::cout << &x << '\t' << x << '\n';
}

scopes_annotated.cpp

/**
 * @file raii.cpp
 * @author Jeffrey Bergamini for CS 19 Boot Camp, jeffrey.bergamini@cabrillo.edu
 *
 * RAII: "Resource acquisition is initialization"
 * Perhaps easier to understand: "scope-based resource management"
 *
 * An object's resources (memory storage, file handles, etc.) are allocated during initialization,
 * and released during destruction. When an object's lifetime ends, its resources should be
 * deallocated/cleaned up/closed/etc.
 *
 * We'll run this through `strace` to verify when files are opened/closed:
 * strace --trace=openat,close ./a.out </srv/datasets/shakespeare-othello.txt
 */
 
#include <cctype>
#include <fstream>
#include <iostream>
 
// Counts and returns the number of English vowel characters in an input stream.
size_t count_vowels(std::istream &source) {
  size_t vowel_count = 0;
  for (char c; source >> c;) {
    c = std::tolower(c);
    if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u')
      ++vowel_count;
  }
  return vowel_count;
}
 
int main() {
  std::ifstream hamlet{"/srv/datasets/shakespeare-hamlet.txt"};
  // Preview of subtype polymorphism: A `std::ifstream` *is a* `std::istream`
  // (i.e., an input stream reading from a file is a specific kind of input stream)
  std::cout << "Hamlet: " << count_vowels(hamlet) << '\n';
  std::cout << "Hamlet again: " << count_vowels(hamlet) << '\n';
  {
    std::ifstream macbeth{"/srv/datasets/shakespeare-macbeth.txt"};
    std::cout << "Macbeth: " << count_vowels(macbeth) << '\n';
    // Lifetime of `macbeth` ends here. File will be closed.
  }
  std::ifstream othello{"/srv/datasets/shakespeare-othello.txt"};
  std::cout << "Othello: " << count_vowels(othello) << '\n';
  // std::cout is just a plain input stream:
  std::cout << "std::cin: " << count_vowels(std::cin) << '\n';
  // Lifetimes of `hamlet` and `othello` end here.
  // Will be closed in the opposite order of initialization (`othello`, then `hamlet`)
}

TBD

TBD

TBD