Compiling and Running C Code

Before you proceed with this page, follow the instructions to set up the course’s RISC-V infrastructure.

Your First C Program

Copy and paste this program into a text file called first.c:

#include <stdio.h> 

int main() {
    printf("Hello, CS 3410!\n");
    return 0;
}

Next, run this command:

$ rv gcc -o first first.c

Here are some things to keep in mind whenever these pages ask you to run a command:

• The $ is not part of the command. This is meant to evoke the command-line prompt in many shells, and it is there to indicate to you that the text that follows is a command that you should run. Do not include the $ when you type the command.
• Our course’s RISC-V infrastructure setup has you create an rv alias for running commands inside the infrastructure container. We will not always include an rv prefix on example commands we list in these pages. Whenever you need to run a tool that comes from the container, use the rv prefix or some other mechanism to make sure the command runs in the container.
• As with all shell commands, it really matters which directory you’re currently “standing in,” called the working directory. Here, first.c and first are both filenames that implicitly refer to files within the working directory. So before running this command, be sure to cd to the place where your first.c file exists.

If everything worked, you can now run this program with this command:

$ rv qemu first
Hello, CS 3410!

(Just type the rv qemu first part. The next line, without the $, is meant to show you what the command should print as output after you hit return.)

This command uses QEMU, an emulator for the RISC-V instruction set, to run the program we just compiled, which is in the file named first.

Recommended Options

While the simple command gcc -o first first.c works fine for this simple example, we officially recommend that you always use a few additional command-line options that make the GCC compiler more helpful. Here are the ones we recommend:

-Wall -Wextra -Wpedantic -Wshadow -Wformat=2 -std=c17

In other words, here’s our complete recommended command for compiling your C code:

$ rv gcc -Wall -Wextra -Wpedantic -Wshadow -Wformat=2 -std=c17 hi.c

Many assignments will include a Makefile that supplies these options for you.

Checking for Common C Errors

Memory-related bugs in C programs are extremely common! The worst thing about them is that they can cause obscure problems silently, without even crashing with a reasonable error message. Fortunately, GCC has built-in tools called sanitizers that can (much of the time, but not always) catch these bugs and give you reasonable error messages.

To use the sanitizers, add these flags to your compiler command:

-g -fsanitize=address -fsanitize=undefined

So here’s a complete compiler command with sanitizers enabled:

$ rv gcc -Wall -Wextra -Wpedantic -Wshadow -Wformat=2 -std=c17 -g -fsanitize=address -fsanitize=undefined hi.c

Then run the resulting program to check for errors.

We recommend trying the sanitizers whenever your code does something mysterious or unpredictable. It’s an unfortunate fact of life that, unlike many other languages, bugs in C code can silently cause weird behavior; sanitizers can help counteract this deeply frustrating problem.