Screenplay: C++: Basic Class

Contents

Code: Code: C++: Basic Class

Plain Old C: No Encapsulation

Prepare directory structure,

.
├── CMakeLists.txt
├── c-point.c
├── c-point.h
└── tests
    ├── CMakeLists.txt
    ├── c-point-tests.cc
    └── run.cc

Instantiation

Steps

• plain C struct point

• test driven (suite C_Point_Tests)

• bulky ops (direct member access)

struct point
{
    int x;
    int y;
};

and a test,

TEST(C_Point_Tests, Instantiation)
{
    struct point p = {1,2};

    ASSERT_EQ(p.x, 1);
    ASSERT_EQ(p.y, 2);
}

Discussion

• Nah

• Direct member access?

• Check for equality? Like p == (1,2), or something?

Move a Point

TEST(C_Point_Tests, Move)
{
    struct point p = {1,2};
    p.x += 3;
    p.y += 3;

    ASSERT_EQ(p.x, 4);
    ASSERT_EQ(p.y, 5);
}

Discussion

• Nah

• p.move(3,3), or something?

Add Points/Vectors?

TEST(C_Point_Tests, Add)
{
    struct point p = {1,2};
    struct point q = {3,4};

    struct point added = {p.x+q.x, p.y+q.y}; // this is not C!

    ASSERT_EQ(added.x, 4);
    ASSERT_EQ(added.y, 6);
}

Discussion

• Nah

Plain Old C: “Methods”

Steps: add tests

• Instantiation_Func: point_create()

  • initially, “forget” to add extern “C”; demonstrate on the fly

  • ah yes, C++. cool.

  TEST(C_Point_Tests, Instantiation_Func)
  {
      struct point p = point_create(1,2);
  
      ASSERT_EQ(p.x, 1);
      ASSERT_EQ(p.y, 2);
  }
  

• Move_Func: point_move()

  • discuss prototype: lhs modified in place - a point is moved

• Add_Func: point_add()

  • discuss prototype: use two points (unmodified) to create new one

• Compare_Func: point_compare()

  • discuss prototype: use int which is C’s boolean

  • yes, memcmp() :-)

C++: class Point

Steps

• add cc-point-tests.cc (and, with the first test, point.{h,cc})

• ctor; member visibility

• move

  • variation: operator+=()

  • discuss: += usually has a value (i += 7)

  • Point& as retval to move() and +=()

  • operator==() (while we are at it)

  • operator!=() (using ASSERT_NE())

• add

• last: inline

Discussion

• public, private (protected?)

• access methods (“properties”?), const

• ctor: initializer list

• add: this