Compilation

> g++ -Wall -Werror units.cpp convert.cpp -o convert

1. Compiler performs preprocessing and compilation on units.cpp and convert.cpp separately: Produces units.o, convert.o
2. The linking phase combines the results of the compilation phase: units.o + convert.o = convert.

Build Phases

# compile source without linking it: `units.o`
> g++ -Wall -Werror -c units.cpp
# output files from each phases: `units.ii`, `units.s`
> g++ -Wall --save-temps -c units.cpp

The Preprocessor

• Performs text-processing operations on each source file
  • Remove all comments
  • Handle preprocessor directives such as #include, #define
• Generate translation unit which compiler actually compiles

The Compiler

• Using translation units, translates it to machine code from C++ code.
• Result is called an object file. (relocatable object file).
  • e.g. units.o, convert.o
  • It's a machine-code instruction but not a runnable program yet.
  • Some obj files doesn't contain definitions of the functions

The Linker

• Combine the object files that generated by the compiler.
• Make sure every functions is defined in some obj files.

std::vector<T>

vector is dynamically-resizeable, growable array.

vector<int> v1;
vector<string> v2(10);

#include <vector>
vector<int> v;
v.push_back(15);
v.push_back(42);
v.push_back(-9);

cout << "Number of elements: " << v.size() << "\n";
for (int i = 0; i < v.size(); ++i)
  cout << "v[" << i << "] = " << v[i] << "\n";

for (int n : v) // C++11 range-based for loop
  cout << " " << n;

Structs

• Struct members are public by default; class members are private by default
• Generally, it used when full functionality of classes isn't required

struct TodoItem { // these members are public
  int id;
  string description;
  bool completed;
};

class TodoList {
  int next_id;
  vector<TodoItem> items;
public:
  int add_task(string description);
  void complete_task(int task_id);
};

C++ allows class/struct declarations to be nested.

class TodoList {
  struct TodoItem {
    // ...
  }
  // ...
}
// TodoItem type isn't visible from the outside of TodoList

Intialize with values:

TodoItem i = {next_id, description, false};

Exception Handling

throw and catch the exception. e.g. out_of_range, regex_error.

double compute_value(double x) {
  if (x < 3.0)
    throw invalid_argument("x must be >= 3");
  return sqrt(x - 3.0);
}

try {
  double v = compute_value(1.0);
  cout << "Answer is "<< v << "\n";
}
catch (invalid_argument) {
  cout << "Error occurred!\n";
}

try {
  double v = compute_value(3.0);
  cout << "Answer is "<< v << "\n";
}
catch (invalid_argument e) {
  cout << "Error occurred!\n";
  cout << e.what() << "\n";
}

Exceptions are as much a part of a function's public interface, as the arguments and the return-value. important to document what exceptions are thrown and the circumstances in which they are thrown.

/**
 * ...
 * Throws invalid_argument if x< 3
 */
double compute_value(double x) {
  // ...
}

Coming up next

• Lecture 3: fstream, scope, pass by value/reference