cpp_tutorial

C++ Tutorial : 

C++ Tutorial Sourabh Jain

Overview : 

Overview Pointers Arrays and strings Parameter passing Class basics Constructors & destructors Class Hierarchy Virtual Functions Coding tips Advanced topics Sourabh Jain

Pointers : 

Pointers int *intPtr; intPtr = new int; *intPtr = 6837; delete intPtr; int otherVal = 5; intPtr = &otherVal; Create a pointer Allocate memory Set value at given address Change intPtr to point to a new location 6837 *intPtr 0x0050 intPtr 5 *intPtr 0x0054 intPtr otherVal &otherVal Deallocate memory Sourabh Jain

Arrays : 

Arrays int intArray[10]; intArray[0] = 6837; int *intArray; intArray = new int[10]; intArray[0] = 6837; ... delete[] intArray; Stack allocation Heap allocation Sourabh Jain

Strings : 

Strings char myString[20]; strcpy(myString, "Hello World"); myString[0] = 'H'; myString[1] = 'i'; myString[2] = '\0'; printf("%s", myString); A string in C++ is an array of characters Strings are terminated with the NULL or '\0' character output: Hi Sourabh Jain

Parameter Passing : 

Parameter Passing int add(int a, int b) { return a+b; } int a, b, sum; sum = add(a, b); pass by value int add(int *a, int *b) { return *a + *b; } int a, b, sum; sum = add(&a, &b); pass by reference Make a local copy of a and b Pass pointers that reference a and b. Changes made to a or b will be reflected outside the add routine Sourabh Jain

Parameter Passing : 

Parameter Passing int add(int &a, int &b) { return a+b; } int a, b, sum; sum = add(a, b); pass by reference – alternate notation Sourabh Jain

Class Basics : 

Class Basics #ifndef _IMAGE_H_ #define _IMAGE_H_ #include <assert.h> #include "vectors.h“ class Image { public: ... private: ... }; #endif Include a library file Include a local file Prevents multiple references Variables and functions accessible from anywhere Variables and functions accessible only from within this class’s functions Sourabh Jain

Creating an instance : 

Creating an instance Image myImage; myImage.SetAllPixels(ClearColor); Image *imagePtr; imagePtr = new Image(); imagePtr->SetAllPixels(ClearColor); ... delete imagePtr; Stack allocation Heap allocation Sourabh Jain

Organizational Strategy : 

Organizational Strategy image.h Header file: Class definition & function prototypes .C file: Full function definitions Main code: Function references image.C main.C void SetAllPixels(const Vec3f &color); void Image::SetAllPixels(const Vec3f &color) { for (int i = 0; i < width*height; i++) data[i] = color; } myImage.SetAllPixels(clearColor); Sourabh Jain

Constructors & Destructors : 

Constructors & Destructors class Image { public: Image(void) { width = height = 0; data = NULL; } ~Image(void) { if (data != NULL) delete[] data; } int width; int height; Vec3f *data; }; Constructor: Called whenever a new instance is created Destructor: Called whenever an instance is deleted Sourabh Jain

Constructors : 

Constructors Image(int w, int h) { width = w; height = h; data = new Vec3f[w*h]; } Constructors can also take parameters Image myImage = Image(10, 10); Image *imagePtr; imagePtr = new Image(10, 10); Using this constructor with stack or heap allocation: stack allocation heap allocation Sourabh Jain

The Copy Constructor : 

The Copy Constructor Image(Image *img) { width = img->width; height = img->height; data = new Vec3f[width*height]; for (int i=0; i<width*height; i++) data[i] = img->data[i]; } Image(Image *img) { width = img->width; height = img->height; data = img->data; } A default copy constructor is created automatically, but it is often not what you want: Sourabh Jain

Passing Classes as Parameters : 

Passing Classes as Parameters bool IsImageGreen(Image img); If a class instance is passed by value, the copy constructor will be used to make a copy. Computationally expensive bool IsImageGreen(Image *img); It’s much faster to pass by reference: bool IsImageGreen(Image &img); or Sourabh Jain

Class Hierarchy : 

Class Hierarchy class Object3D { Vec3f color; }; class Sphere : public Object3D { float radius; }; class Cone : public Object3D { float base; float height; }; Child classes inherit parent attributes Object3D Sphere Cone Sourabh Jain

Class Hierarchy : 

Class Hierarchy Sphere::Sphere() : Object3D() { radius = 1.0; } Child classes can call parent functions Child classes can override parent functions class Object3D { virtual void setDefaults(void) { color = RED; } }; class Sphere : public Object3D { void setDefaults(void) { color = BLUE; radius = 1.0 } }; Call the parent constructor Superclass Subclass Sourabh Jain

Virtual Functions : 

Virtual Functions class Object3D { virtual void intersect(Ray *r, Hit *h); }; class Sphere : public Object3D { virtual void intersect(Ray *r, Hit *h); }; myObject->intersect(ray, hit); If a superclass has virtual functions, the correct subclass version will automatically be selected Sphere *mySphere = new Sphere(); Object3D *myObject = mySphere; A superclass pointer can reference a subclass object Actually calls Sphere::intersect Superclass Subclass Sourabh Jain

Pure Virtual Functions : 

Pure Virtual Functions class Object3D { virtual void intersect(Ray *r, Hit *h) = 0; }; A pure virtual function has a prototype, but no definition. Used when a default implementation does not make sense. A class with a pure virtual function is called a pure virtual class and cannot be instantiated. (However, its subclasses can). Sourabh Jain

The main function : 

The main function int main(int argc, char** argv); This is where your code begins execution Number of arguments Array of strings argv[0] is the program name argv[1] through argv[argc-1] are command-line input Sourabh Jain

Coding tips : 

Coding tips #define PI 3.14159265 #define MAX_ARRAY_SIZE 20 Use the #define compiler directive for constants printf("value: %d, %f\n", myInt, myFloat); cout << "value:" << myInt << ", " << myFloat << endl; Use the printf or cout functions for output and debugging assert(denominator != 0); quotient = numerator/denominator; Use the assert function to test “always true” conditions Sourabh Jain

Coding tips : 

Coding tips delete myObject; myObject = NULL; After you delete an object, also set its value to NULL (This is not done for you automatically) This will make it easier to debug memory allocation errors assert(myObject != NULL); myObject->setColor(RED); Sourabh Jain

Segmentation fault (core dumped) : 

Segmentation fault (core dumped) int intArray[10]; intArray[10] = 6837; Image *img; img->SetAllPixels(ClearColor); Typical causes: Access outside of array bounds Attempt to access a NULL or previously deleted pointer These errors are often very difficult to catch and can cause erratic, unpredictable behavior. Sourabh Jain

Common Pitfalls : 

Common Pitfalls void setToRed(Vec3f v) { v = RED; } Since v is passed by value, it will not get updated outside of The set function The fix: void setToRed(Vec3f &v) { v = RED; } void setToRed(Vec3f *v) { *v = RED; } or Sourabh Jain

Common Pitfalls : 

Common Pitfalls Sphere* getRedSphere() { Sphere s = Sphere(1.0); s.setColor(RED); return &s; } C++ automatically deallocates stack memory when the function exits, so the returned pointer is invalid. The fix: Sphere* getRedSphere() { Sphere *s = new Sphere(1.0); s->setColor(RED); return s; } It will then be your responsibility to delete the Sphere object later. Sourabh Jain

Advanced topics : 

Advanced topics Lots of advanced topics, but few will be required for this course friend or protected class members inline functions const or static functions and variables compiler directives operator overloading Vec3f& operator+(Vec3f &a, Vec3f &b); Sourabh Jain