94 lines
5.1 KiB
Markdown
94 lines
5.1 KiB
Markdown
---
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title: C++ Compilers
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---
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# Intro to C++ Compilers
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In order to get started with C++, you will need to learn a little about compilers and how C++ runs on your computer.
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When all is said and done, computers only understand one language, machine language. Machine language is entirely made up of
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binary bits, or 0s and 1s. While it would be possible to program in binary, it would be incredibly tedious and time consuming.
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So, we humans developed programming languages to make it easier to develop software. Assembly language is a direct 1 to 1 with machine
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language. Languages like C, C++, and COBOL are a little higher and need to be compiled down. It goes even higher. Languages
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like JavaScript and Python have components that get translated into C++ or other low level languages before they get compiled,
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effectively making them "higher" languages than C or C++.
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Because computer architecture is made up of electronic switches and cables that can only work with binary 1s and 0s,
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you need a compiler to translate your code from high level C++ to machine language that the CPU can understand.
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Compilers are utility programs that take your code and transform it into executable machine code files. When you run a compiler
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on your code, first, the preprocessor reads the source code (the C++ file you just wrote). The preprocessor searches for any
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preprocessor directives (lines of code starting with a #). Preprocessor directives cause the
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preprocessor to change your code in some way (by usually adding some library or another C++ file).
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Next, the compiler works through the preprocessed code line by line translating
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each line into the appropriate machine language instruction. This will also uncover any syntax errors that are present in your
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source code and will throw an error to the command line. Finally, if no errors are present, the compiler creates an object
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file with the machine language binary necessary to run on your machine. While the object file that the compiler just created
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is likely enough to do something on your computer, it still isn't a working executable of your C++ program. There is a final
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important step to reach an executable program.
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C++ contains a vast library to aid in performing difficult tasks like I/O and hardware manipulation. You can include these
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libraries with preprocessor directives, but the preprocessor doesn't automatically add them to your code. In order for you to have
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a final executable program, another utility known as the linker must combine your object files with the library functions
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necessary to run the code. Think of it as having all the necessary blocks
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to build a house. The compiler made all the blocks but the linker is the one that sticks them all together to finally create a house.
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Once this is done, you now have a functioning executable file!
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## How to Compile a file
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Let's say you have a C++ file called `helloWorld.cpp` ...
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### If you are on Windows --
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#### Using and IDE like CodeBlocks
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It is as simple as clicking the build and run buttons, they will create a file in the project folder.
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#### Using Command Prompt
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1. Open a Developer Command Prompt - For this step, you will need to have Microsoft Visual Studio or some other IDE that
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enables you to compile your program from the command line. You can also search online for C++ compilers.
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2. Navigate to the source code directly
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3. Run the Compiler on your source code (assuming you are using the Microsoft Visual Studio compiler)
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`cl /EHsc helloWorld.cpp`
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This will now create an object file and automatically link it for you. If you look in that same folder, you will see a
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hellWorld.exe executable file (note the exe extension) is now present.
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4. Type `helloWorld` into the prompt to run the executable
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Alternatively, many IDEs allow for quick building and viewing of your program. This may be easier since your version of
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windows may not come pre packaged with a compiler utility.
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### If you are on Linux or OSX --
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1. Open up a terminal window and navigate to the source code directory
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2. Run the Compiler on your source code
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`g++ helloWorld.cpp -o helloWorld`
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This will create an object file and automatically link it for you. Look in the folder and you will see a helloWorld.exe
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executable file (note the exe extension).
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3. Type `./helloWorld` in the terminal window to run the executable file
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g++ is the standard Linux compiler and is a great utility. It comes packaged with the operating system.
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NOTE:
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to compile and execute your code directly, run
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`g++ -o helloWorld helloWorld.cpp; ./helloWorld`
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so when you need to compile and run your code multiple times,
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up arrow-enter
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### Adding Flags
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You can also add flags to the compiler to your custom and favor. For example:
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`g++ -O2 helloWorld.cpp -o helloWorld`
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Some common flags is :
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1. -O2 : Optimize your code, so it may run faster
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2. -std=c++11 : use c++11 instead of c++98 which is defaulted.
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3. -Wall: prompt some warning about some common mistakes which can bug your program.
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4. -Wextra: prompt some extra warning.
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____________
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There are a number of different types of compilers. The two listed are the two that are usually packaged with the Windows
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or Linux/OSX.
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