C++ Intro: Object-Oriented Programming & Code::Blocks IDE, Study notes of History

Download C++ Intro: Object-Oriented Programming & Code::Blocks IDE and more Study notes History in PDF only on Docsity! Introduction to C++: Part 1 tutorial version 0.2 Brian Gregor Research Computing Services Getting started with the room B27 terminals  Log on with your BU username  On the desktop is a Training Files folder. Open it and go to the subfolder: RCS_Tutorials\Tutorial Files\Introduction to C++  Copy the CodeBlocks Projects folder to your desktop. Tutorial Outline: Part 1  Very brief history of C++  Definition object-oriented programming  When C++ is a good choice  The Code::Blocks IDE  Object-oriented concepts  First program!  Some C++ syntax  Function calls  Create a C++ class Very brief history of C++ For details more check out A History of C++: 1979−1991 C C++ Object-oriented programming  Object-oriented programming (OOP) seeks to define a program in terms of the things in the problem (files, molecules, buildings, cars, people, etc.), what they need, and what they can do. • Data: • molecular weight, structure, common names, etc. • Methods: • IR(wavenumStart, wavenumEnd) : return IR emission spectrum in range class GasMolecule GasMolecule ch4 GasMolecule co2 spectrum = ch4.IR(1000,3500) Name = co2.common_name Objects (instances of a class) “pseudo-code” When to choose C++  Despite its many competitors C++ has remained popular for ~30 years and will continue to be so in the foreseeable future.  Why?  Complex problems and programs can be effectively implemented  OOP works in the real world!  No other language quite matches C++’s combination of performance, expressiveness, and ability to handle complex programs.  Choose C++ when:  Program performance matters  Dealing with large amounts of data, multiple CPUs, complex algorithms, etc.  Programmer productivity is less important  It is faster to produce working code in Python, R, Matlab or other scripting languages!  The programming language itself can help organize your code  Ex. In Matlab almost everything is a vector or matrix.  Access to libraries that will help with your problem  Ex. Nvidia’s CUDA Thrust library for GPUs  Your group uses it already! “If you’re not at all interested in performance, shouldn’t you be in the Python room down the hall?” ― Scott Meyers (author of Effective Modern C++) Code::Blocks  In this tutorial we will use the Code::Blocks integrated development environment (IDE) for writing and compiling C++  Run it right on the terminal or on the SCC (module load codeblocks)  About C::B  cross-platform: supported on Mac OSX, Linux, and Windows  Oriented towards C, C++, and Fortran, supports others such as Python  Short learning curve compared with other IDEs such as Eclipse or Visual Studio  Has its own automated code building system, so we can concentrate on C++  It can convert its build system files to make and Makefiles so you are not tied to C::B  Project homepage: http://www.codeblocks.org IDE Advantages  Handles build process for you  Syntax highlighting and live error detection  Code completion (fills in as you type)  Creation of files via templates  Built-in debugging  Code refactoring (ex. Change a variable name everywhere in your code)  Higher productivity IDEs available on the SCC  Code::Blocks (used here)  geany – a minimalist IDE, simple to use  Eclipse – a highly configurable, adaptable IDE. Very powerful but with a long learning curve  Spyder – Python only, part of Anaconda Some Others  Xcode for Mac OSX  Visual Studio for Windows  NetBeans (cross platform)  Step 2. Choose the Console category and then the Console application and click Go.  Step 3: Click Next on the “Welcome to the new console application wizard!” screen.  Step 4: Choose C++!  …then click Next.  Step 5. Enter a project title. Let C::B fill in the other fields for you. If you like you can change the default folder to hold the project. Click Next.  Step 8: Your project is now created! Click on Sources in the left column, then double-click main.cpp.  Click the icon in the toolbar or press F9 to compile and run the program. Hello, World!  Console window:  Build and compile messages Behind the Scenes: The Compilation Process header files iostream.h my_headerh (ee) * Expanded source code file * not normally visible * g++-E to see output C++ preprocessor C++ compiler main.cpp “ ~ * Assembler code file * not normally visible * g++-Sto see output Object code file main.o C++ library files system library files assembler Executable linker Q++ -o main main.cpp main Header Files  C++ (along with C) uses header files as to hold definitions for the compiler to use while compiling.  A source file (file.cpp) contains the code that is compiled into an object file (file.o).  The header (file.h) is used to tell the compiler what to expect when it assembles the program in the linking stage from the object files.  Source files and header files can refer to any number of other header files. #include <iostream> using namespace std; int main() { string hello = "Hello"; string world = "world!"; string msg = hello + " " + world ; cout << msg << endl; msg[0] = 'h'; cout << msg << endl; return 0; } C++ language headers aren’t referred to with the .h suffix. <iostream> provides definitions for I/O functions, including the cout function. Slight change  Let’s put the message into some variables of type string and print some numbers.  Things to note:  Strings can be concatenated with a + operator.  No messing with null terminators or strcat() as in C  Some string notes:  Access a string character by brackets or function:  msg[0]  “H” or msg.at(0)  “H”  C++ strings are mutable – they can be changed in place.  Press F9 to recompile & run. #include <iostream> using namespace std; int main() { string hello = "Hello"; string world = "world!"; string msg = hello + " " + world ; cout << msg << endl; msg[0] = 'h'; cout << msg << endl; return 0; } A first C++ class: string  string is not a basic type (more on those later), it is a class.  string hello creates an instance of a string called “hello”.  hello is an object.  Remember that a class defines some data and a set of functions (methods) that operate on that data.  Let’s use C::B to see what some of these methods are…. #include <iostream> using namespace std; int main() { string hello = "Hello"; string world = "world!"; string msg = hello + " " + world ; cout << msg << endl; msg[0] = 'h'; cout << msg << endl; return 0; } A first C++ class: string  Start typing “msg.size()” until it appears in the list. Once it’s highlighted (or you scroll to it) press the Tab key to auto-enter it.  On the right you can click “Open declaration” to see how the C++ compiler defines size(). This will open basic_string.h, a built-in file. A first C++ class: string  Tweak the code to print the number of characters in the string, build, and run it.  From the point of view of main(), the msg object has hidden away its means of tracking and retrieving the number of characters stored.  Note: while the string class has a huge number of methods your typical C++ class has far fewer! #include <iostream> using namespace std; int main() { string hello = "Hello" ; string world = "world!" ; string msg = hello + " " + world ; cout << msg << endl ; msg[0] = 'h'; cout << msg << endl ; cout << msg.size() << endl ; return 0; }  Note that cout prints integers without any modification!  More on this behavior later. Basic Syntax  C++ syntax is very similar to C, Java, or C#. Here’s a few things up front and we’ll cover more as we go along.  Curly braces are used to denote a code block (like the main() function): { … some code … }  Statements end with a semicolon:  Comments are marked for a single line with a // or for multilines with a pair of /* and */ :  Variables can be declared at any time in a code block. void my_function() { int a ; a=1 ; int b; } int a ; a = 1 + 3 ; // this is a comment. /* everything in here is a comment */ Built-in (aka primitive or intrinsic) Types  “primitive” or “intrinsic” means these types are not objects  Here are the most commonly used types.  Note: The exact bit ranges here are platform and compiler dependent!  Typical usage with PCs, Macs, Linux, etc. use these values  Variations from this table are found in specialized applications like embedded system processors. Name Name Value char unsigned char 8-bit integer short unsigned short 16-bit integer int unsigned int 32-bit integer long unsigned long 64-bit integer bool true or false Name Value float 32-bit floating point double 64-bit floating point long long 128-bit integer long double 128-bit floating point http://www.cplusplus.com/doc/tutorial/variables/ Need to be sure of integer sizes?  In the same spirit as using integer(kind=8) type notation in Fortran, there are type definitions that exactly specify exactly the bits used. These were added in C++11.  These can be useful if you are planning to port code across CPU architectures (ex. Intel 64-bit CPUs to a 32-bit ARM on an embedded board) or when doing particular types of integer math.  For a full list and description see: http://www.cplusplus.com/reference/cstdint/ Name Name Value int8_t uint8_t 8-bit integer int16_t uint16_t 16-bit integer int32_t uint32_t 32-bit integer int64_t uint64_t 64-bit integer #include <cstdint> Reference and Pointer Variables  Variable and object values are stored in particular locations in the computer’s memory.  Reference and pointer variables store the memory location of other variables.  Pointers are found in C. References are a C++ variation that makes pointers easier and safer to use.  More on this topic in Part 2. string hello = "Hello"; string *hello_ptr = &hello; string &hello_ref = hello; The object hello occupies some computer memory. The asterisk indicates that hello_ptr is a pointer to a string. hello_ptr variable is assigned the memory address of object hello which is accessed with the “&” syntax. The & here indicates that hello_ref is a reference to a string. The hello_ref variable is assigned the memory address of object hello automatically. Type Casting cont’d  const_cast<new type>( expression )  Variables labeled as const can’t have their value changed.  const_cast lets the programmer remove or add const to reference or pointer type variables.  If you need to do this, you probably need to re-think your code.  reinterpret_cast<new type>( expression )  Takes the bits in the expression and re-uses them unconverted as a new type. Also only works on reference or pointer type variables.  Sometimes useful when reading in binary files and extracting parameters. “unsafe”: the compiler will not protect you here and the programmer must make sure everything is correct! Danger! Functions  Open the project “FunctionExample” in C::B files  Compile and run it!  Open main.cpp  4 function calls are listed.  The 1st and 2nd functions are identical in their behavior.  The values of L and W are sent to the function, multiplied, and the product is returned.  RectangleArea2 uses const arguments  The compiler will not let you modify their values in the function.  Try it! Uncomment the line and see what happens when you recompile.  The 3rd and 4th versions pass the arguments by reference with an added & float RectangleArea1(float L, float W) { return L*W ; } float RectangleArea2(const float L, const float W) { // L=2.0 ; return L*W ; } float RectangleArea3(const float& L, const float& W) { return L*W ; } void RectangleArea4(const float& L, const float& W, float& area) { area= L*W ; } The function arguments L and W are sent as type float. Product is computed The return type is float. Using the C::B Debugger  To show how this works we will use the C::B interactive debugger to step through the program line-by-line to follow the function calls.  Make sure you are running in Debug mode. This turns off compiler optimizations and has the compiler include information in the compiled code for effective debugging.