Command Line Navigation and Compiling

Command Line Navigation and Compiling 
 
You should become familiar with how to compile and work from the command line. Below is a quick reference and 
instructions on how to use the gcc c++ compiler (g++) from the Windows command line. g++ is included as part of the 
QTCreator bundled download. If you are on a Mac/Linux box, some commands will differ, but many will be the same.  
 
Contents 
Opening a command prompt: ................................................................................................................................................. 1 
Command line quick reference: .............................................................................................................................................. 2 
Path (Windows):...................................................................................................................................................................... 3 
Using g++: ................................................................................................................................................................................ 5 
g++ Options: ............................................................................................................................................................................ 6 
Redirection: ............................................................................................................................................................................. 6 
 
 
 
Opening a command prompt: 
Windows : You can use either the traditional Command Prompt or PowerShell. To open, go to the start menu and search 
for either "Command Prompt" or "PowerShell". 
You can shift-right click inside a folder in Windows and get an option to "Open command prompt here" (may be "Open 
PowerShell window here" on more recent versions of Windows) 
 
Mac : Use spotlight to search for Terminal and open a terminal window. From in finder you can also open a Terminal 
window at the location you are viewing. 
 
   

Command line quick reference:

Goal

Command

Example:

Switch to different drive

Windows only

DriveLetter:

Change into a subdirectory

cd directoryname

cd cs161

Go up a directory level

cd ..

Go to top level of this drive

-For Mac/Linux

cd \

cd /

See what is in this directory

-For Mac/Linux

-Mac/Linux see more info

dir

ls -la

dir

See only files of certain type

-For Mac/Linux

dir *.extension

ls *.extension

dir *.cpp

ls *.cpp

See the contents of a file

-For Mac/Linux

type filename

less filename

type main.cpp

less main.cpp

Compile a file

SEE G++ SECTION

g++ filename -o program.exe

g++ main.cpp -o myprogram.exe

Run a program

-For Mac/Linux

PROGRAM MUST BE ON PATH OR IN

CURRENT DIRECTORY

programName.exe

./programName.exe

myprogram.exe

./myprogram.exe

Windows Path:

See PATH

SEE PATH SECTION

echo %PATH% (Command Prompt)

Speeding things up:

In most places times, pressing tab will try to autocomplete what you have typed so far. Hit tab multiple times to cycle

through possible completions.

Use up arrow and down arrow to reuse recently typed commands.

Path (Windows):

Mac and Linux also use a PATH, but you should not need to edit them by hand.

The path is the collection of directories where Windows looks for programs when you try to execute a program with a

command like "main.exe" or "g++". It is stored in a variable called PATH - it is just a list of directories separated with

semicolons:

C:\Program Files (x86)\Java\jdk1.7.0_07\bin;C:\Cygwin\bin;…

To see your current path, type “PATH”

The path always includes the current folder. That is where Windows will look first for the program you tried to run. If it is

not found, each directory in the PATH is checked to see if the program is there.

To get the c++ compiler working you need to make sure the folder containing g++ is on your path. It will be in the QT

folder in a directory like C:\Qt\ \Tools\mingw530_32\bin. The exact version number (530_32) may be different,

but it should be in a similar place (C:\QT\ Tools\mingwxx_xx\bin). Make sure you see g++ in that folder. This will be the

folder you need to add to the path:

To permanently add this folder to your path so every command prompt window can make use of g++ automatically, you

need to change the environmental variables. Open the control panel and search for "system" or "environment", find the

Edit system environment variables panel:

Then click Environmental Variables.

Under the System variables section, find Path and edit it:

The way to edit the path depends on how recent your version of Windows is:

Newer (shows path in window below)

This window the path up into a list of folders. Simply click

New and then type:

C:\Qt\Tools\mingw530_32\bin

(or wherever your g++ is located)

Older (shows path in window below)

Scroll to the end of the variable value and add

;C:\Qt\Tools\mingw530_32\bin

(or wherever your g++ is located)

The semicolon is important to separate the new folder

name from everything that comes before it.

Something like this:

You may find it easier to copy the text out to notepad, edit

it there and then paste it back in.

Using g++:

Windows: To run g++ you must tell Windows where to find it - see Path section above first.

Mac: The compiler you will use is called clang. But, it sets itself up to "hijack" calls to g++

So you can still just type g++ or you can type clang++.

g++ run by itself will tell you "no input files"

g++ -c filename.cpp will compile your file into an object file filename.o

The –c says “Compile only”, do not link into a final executable program. Try this and then look for the resulting new file.

g++ filename.o will link your object file with any libraries or other code it needs and produce an executable a.exe. Try

this and look for the new exe

Technically we are using the linker program "ld"… but g++ calls it for us with some extra options set

To run your program, type a.exe On Linux/Mac, type ./a

g++ filename.cpp will assume you want to compile and link your object file in one step to directly produce an executable

a.exe

To give your executable file a better name than a.exe, use the -o flag:

g++ filename.o -o executablename

Something like:

g++ main.o -o myProgram.exe

To go directly from cpp file to final program, (compile and link code all at once), do:

g++ main.cpp -o myProgram.exe

This performs all the steps of compiling main.cpp. Then you can run your program by typing "myProgram.exe" On

Mac/Linux don't forget to put ./ before the program name.

For more complete details on compiling from the command line, refer to section 1.3-1.5 of this reference:

http://www3.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make.html

g++ Options:

g++ supports many options. Simply include them after g++:

g++ -g -Wall -std=c++11 main.cpp -o myProgram.exe

Here are some important ones to recognize:

-g

Compile with debug information built in. Necessary for meaningful

debugging but does bloat executable, make it much slower to run and

makes it easier for others to reverse engineer.

-std=c++11

Compiles the code using the more modern 2011 version of the C++ spec

(instead of the ancient one)

-O0

Capital Oh followed by zero. No optimization (default)

-O2

All reasonable code optimizations - compile time is slower, but

program will run significantly faster (building release in

QTCreator).

-O3

Even more optimization - these may make the executable much larger

in an effort to speed things up.

-Wall

Turn on most warnings.

-o

Output file name.

-c

Create object files – do not link into application.

-S

Output an assembly file instead of compiling to machine code.

-E

Just run preprocessor and dump to console with notes about what line

numbers code came from. -E -P skips line numbers.

-Ifolder

Look in given folder (may be relative using . or .. or absolute

starting with C:…) for header files that are included.

-Lfolder

Look in given folder for library files needed.

-lfolder

Lower-case L : library to link against.

In general, they can go in any order. If two things conflict (-O0 and -O3), last one usually wins.

Redirection:

Allow you to send program output to a file or a file's contents to a program. (See

http://www.cs.princeton.edu/courses/archive/spr05/cos126/cmd-prompt.html for more details).

myProgram.exe > out.txt

Run myProgram.exe and whatever it prints send to the file out.txt instead of the console. (If the file exists already,

overwrite it). This includes any input prompts… you have to know what needs to be typed in as input to the program and

do so without the prompts!

myProgram.exe >> out.txt

Run myProgram.exe and whatever it prints ADD to the end of file out.txt instead of the console. (If the file does not

exist, make it).

myProgram.exe < in.txt

Run myProgram.exe and whenever it needs input, get it from in.txt instead of the console.

myProgram.exe 2> error.txt

Run myProgram.exe and whatever error messages it prints send to the file error.txt instead of the console. This is handy

for storing compiler error messages that g++ gives. Something like:

g++ myBadFile.cpp -o myProgram.exe 2> error.txt