Setup

Ahh, step 1. Don’t you love a fresh start on a blank slate? And then selecting that singular brick onto which you will build your entire palatial estate?

Unfortunately, when you’re building a computer program, step 1 can get… complicated. And frustrating. You have to make sure your environment is set up for the programming language you’re using, and you have to figure out how to compile and run your program in that environment.

Fortunately, the program we are building doesn’t depend on any external libraries, so you don’t need anything beyond a C compiler and the standard library it comes with. (We will also be using the make program.) To check whether you have a C compiler installed, try running cc --version at the command line (cc stands for “C Compiler”). To check whether you have make, try running make -v.

How to install a C compiler…

…in Windows

You will need to install some kind of Linux environment within Windows. This is because our text editor interacts with the terminal at a low level using the <termios.h> header, which isn’t available on Windows. I suggest using either Bash on Windows or Cygwin.

Bash on Windows: Only works on 64-bit Windows 10. See the installation guide. After installing it, run bash at the command line whenever you want to enter the Linux environment. Inside bash, run sudo apt-get install gcc make to install the GNU Compiler Collection and the make program. If sudo takes a really long time to do anything, you may have to fix your /etc/hosts file.

Cygwin: Download the installer from cygwin.com/install.html. When the installer asks you to select packages to install, look in the devel category and select the gcc-core and make packages. To use Cygwin, you have to run the Cygwin terminal program. Unlike Bash on Windows, in Cygwin your home directory is separate from your Windows home directory. If you installed Cygwin to C:\cygwin64, then your home directory is at C:\cygwin64\home\yourname. So if you want to use a text editor outside of Cygwin to write your code, that’s where you’ll want to save to.

…in macOS

When you try to run the cc command, a window should pop up asking if you want to install the command line developer tools. You can also run xcode-select --install to get this window to pop up. Then just click “Install” and it will install a C compiler and make, among other things.

…in Linux

In Ubuntu, it’s sudo apt-get install gcc make. Other distributions should have gcc and make packages available as well.

The main() function

Create a new file named kilo.c and give it a main() function. (kilo is the name of the text editor we are building.)

int main() {
  return 0;
}

In C, you have to put all your executable code inside functions. The main() function in C is special. It is the default starting point when you run your program. When you return from the main() function, the program exits and passes the returned integer back to the operating system. A return value of 0 indicates success.

C is a compiled language. That means we need to run our program through a C compiler to turn it into an executable file. We then run that executable like we would run any other program on the command line.

To compile kilo.c, run cc kilo.c -o kilo in your shell. If no errors occur, this will produce an executable named kilo. -o stands for “output”, and specifies that the output executable should be named kilo.

To run kilo, type ./kilo in your shell and press Enter. The program doesn’t print any output, but you can check its exit status (the value main() returns) by running echo $?, which should print 0.

Compiling with make

Typing cc kilo.c -o kilo every time you want to recompile gets tiring. The make program allows you to simply run make and it will compile your program for you. You just have to supply a Makefile to tell it how to compile your program.

Create a new file literally named Makefile with the following contents.

kilo: kilo.c
	$(CC) kilo.c -o kilo -Wall -Wextra -pedantic -std=c99

The first line says that kilo is what we want to build, and that kilo.c is what’s required to build it. The second line specifies the command to run in order to actually build kilo out of kilo.c. Make sure to indent the second line with an actual tab character, and not with spaces. You can indent C files however you want, but Makefiles must use tabs.

We have added a few things to the compilation command:

• $(CC) is a variable that make expands to cc by default.
• -Wall stands for “all Warnings”, and gets the compiler to warn you when it sees code in your program that might not technically be wrong, but is considered bad or questionable usage of the C language, like using variables before initializing them.
• -Wextra and -pedantic turn on even more warnings. For each step in this tutorial, if your program compiles, it shouldn’t produce any warnings except for “unused variable” warnings in some cases. If you get any other warnings, check to make sure your code exactly matches the code in that step.
• -std=c99 specifies the exact version of the C language standard we’re using, which is C99. C99 allows us to declare variables anywhere within a function, whereas ANSI C requires all variables to be declared at the top of a function or block.

Now that we have a Makefile, try running make to compile the program.

It may output make: `kilo' is up to date.. It can tell that the current version of kilo.c has already been compiled by looking at each file’s last-modified timestamp. If kilo was last modified after kilo.c was last modified, then make assumes that kilo.c has already been compiled, and so it doesn’t bother running the compilation command. If kilo.c was last modified after kilo was, then make recompiles kilo.c. This is more useful for large projects with many different components to compile, as most of the components shouldn’t need to be recompiled over and over when you’re only making changes to one component’s source code.

Try changing the return value in kilo.c to a number other than 0. Then run make, and you should see it compile. Run ./kilo, and try echo $? to see if you get the number you changed it to. Then change it back to 0, recompile, and make sure it’s back to returning 0.

After each step in this tutorial, you will want to recompile kilo.c, see if it finds any errors in your code, and then run ./kilo. It is easy to forget to recompile, and just run ./kilo, and wonder why your changes to kilo.c don’t seem to have any effect. You must recompile in order for changes in kilo.c to be reflected in kilo.

In the next chapter, we’ll work on getting the terminal into raw mode, and reading individual keypresses from the user.