Outline

1. Linux Introduction

2. C++ syntax

what we will learn

• how to work in Linux
• How to write software with modern c++
• core software development techniques
• how to work with image using OpenCV
• how to implement inverse image search

Check out Google Image search for example: https://images.google.come/

why C++? why Linux? Why?

• over 50000 developers surveyed
• nearly half of them use linux
• C++ is the most used systems language(4.5 million users in 2015)
• All companies want C++ in our field.

What is Linux?

• Linux is a free Unix-like OS
• Linux kernel implemented by Linus Torvalds.
• Extremely popular: Android, ChromeOS, servers, supercomputers.
• use any distribution if we have preference

Linux Directory tree

• Tree organization starting with root: /
• There are no volume letters, e.g. C:, D:
• User can only access his/her own folder

Understanding files and folders

• Folders end with / e.g. /path/folder/
• Everything else is files, e.g. /path/file
• Absolute paths start with / while all other paths are relative:
  • /home/igor/folder/ — absolute path to a folder
  • /home/igor/file.cpp — absolute path to a file
  • folder/file — relative path to a file
• Paths are case sensitive:
  • filename is different from FileName
• Extension is part of a name:
  • filename.cpp is different from filename.png

Linux Terminal

• Press Ctrl + Alt + T to open terminal
• Linux terminal is a very powerful tool
• Most tasks can be done faster from the terminal than from the GUI

Navigating tree from terminal

• Terminal is always in some folder
• pwd: print working directory
• cd : change directory to
• ls : list contents of a directory
• Special folders:
  • / — root folder
  • ~ — home folder
  • . — current folder
  • .. — parent folder

Structure of Linux commands

Typical structure

${PATH}/command [ options ] [ parameters ]

• ${PATH}/command: absolute or relative path to the program binary
• • e.g. -h, or –help
• • e.g. input files, etc.

Use help with Linux programs

• man — manual
  • exhaustive(철저한) manual on program usage
• command -h
• command –help
  • usually shorter help message

Using command completion

Pressing [tab] while typing:

• completes name of a file, folder or program
• “beeps” if current text does not match any file or folder uniquely Pressing [tab] + [tab] shows all potential matches

Example :

Creating and manipulating files and folders

• mkdir [-p] — make directory
  • Create a folder (with all parent folders [-p])
• rm [-r] — remove [recursive]
  • Remove file or folder (With folder contents [-r])
• cp [-r] — copy
  • Copy file or folder from to
• mv — move
  • Move file or folder from to

Using placeholders

• Can be used with most of terminal commands: ls, rm, mv etc.

Example

Standard input/output channels

• Single input channel: stdin
• Two output channels:
  • stdout: Standard output: channel 1
  • stderr: Standard error output: channel 2
• Redirecting stdout
  • command 1> out.txt
  • command » out.txt
• Redirecting stderr
  • command 2> out.txt
• Redirect stdout and stderr into a file
  • progamm > out.txt 2>&1
• Write stdout and stderr into different files
  • progamm 1>stdout.txt 2>stderr.txt

Working with files

• more/less/cat
  • Most of the time using cat if enough
• find -name
  • Search for file in folder
  • , allows wildcards
• grep
  • Search for a string in a file

Chaining commands

• command1; command2; command3
  • Calls commands one after another
• command1 && command2 && command3
  • Same as above but fails if any of the commands returns a non-zero code

• command1

  command2

  command3

  • Pipe stdout of command1 to stdin of command2 and stdout of command2 to stdin of command3
• Piping commonly used with grep:

  • ls	grep smth look for smth in output of ls

Canceling commands

• CTRL + C
  • Cancel currently running command
• kill -9
  • Kill the process with id pid
• killall
  • Kill all processes with name pname
• htop (top)
  • Shows an overview of running processes
  • Allows to kill processes by pressing F9

    Command history

• The shell saves the history of commands in the ~/.bash_history file

Installing software

Most of the software is available in the system repository. To install a program in Ubuntu type this into terminal:

• sudo apt update to update information about available packages
• **sudo apt install ** to install the program that you want
• **Use apt search ** to find all packages that provide
• Same for any library, just with lib prefix

where to write C++ code

Good code style

Programs are meant to be read by humans and only incidentally for computers to execute. - Donald Knuth

• Use clang_format to format your code
• use cpplint to check the style
• Following a style guide will save you time and make the code more readable
• We use Google Code Style Sheet
• Naming and style recommendations will be marked by GOOGLE-STYLE tag in slides

Everything starts with main

• Every C++ program starts with main
• main is a function that returns an error code
• Error code 0 means OK
• Error code can be any number in [1, 255]

#include directive

Two variants:

• #include — system include files
• #include “file” — local include files
  • Copies the content of file into the current file

I/O streams for simple input and output

• Handle stdin, stdout and stderr:
  • std::cin — maps to stdin
  • std::cout — maps to stdout
  • std::cerr — maps to stderr
• #include to use I/O streams
• #include <bits/strc++> to use I/O streams
• Part of C++ standard library

Compile and run Hello World!

• We understand text
• Computer understands machine code
• Compilation is translation from text to machine code
• Compilers we can use on Linux:
  • GCC
  • Clang [*] [used in examples]
• Compile and run Hello World example:

Reference

https://www.ipb.uni-bonn.de/teaching/modern-cpp/

Cpp Core Guidelines: https://github.com/isocpp/CppCoreGuidelines

Git guide: http://rogerdudler.github.io/git-guide/

C++ Tutorial: http://www.cplusplus.com/doc/tutorial/

Book: Code Complete 2 by Steve McConnell