C++ Beginner · Lesson 01 of 22

Compilers & the build process

GCC, Clang and MSVC; what happens between source code and a running program.

Estimated time · 45–75 min

Learning goals

What you will understand

Explain compilers & the build process in your own words
Use it in a small robotics example
Verify the result instead of assuming it worked

Understand the idea first

The mental model

C++ source code is not run directly. A compiler translates it to machine code. GCC (g++) and Clang (clang++) are the usual compilers on Ubuntu and are what ROS 2 uses; MSVC is Microsoft's compiler on Windows. They accept the same language, but their warnings and error messages differ, so it helps to try both.

This course uses C++17. Always tell the compiler the standard with -std=c++17 and turn warnings on with -Wall -Wextra -Wpedantic. Warnings are early feedback: fix them from the first build.

Guided lesson

Work through these steps

1.
Read the compilers & the build process example and identify what each line owns or changes.
2.
Create a small source file, compile with -std=c++17 and warnings enabled, and run it.
3.
Change one input, predict the result before running, then compare the output.
4.
Record one compiler or runtime error and explain the correction in your own words.

Worked example

Read it before you run it

g++ --version
# Print the GCC version; C++17 needs GCC 7 or newer.
clang++ --version
# Print the Clang version (optional; install with sudo apt install clang).
g++ -std=c++17 -Wall -Wextra -Wpedantic main.cpp -o robot_app
# Compile main.cpp as C++17 with extra warnings; -o names the executable robot_app.
clang++ -std=c++17 -Wall -Wextra main.cpp -o robot_app_clang
# Build the same file with Clang and compare its messages with GCC's.
./robot_app
# Run the program you built from the current folder (./ means 'this folder').
echo $?
# Print the exit code of the last command; 0 means the program reported success.

What the example is doing

1.Read declarations from right to left: identify each value's type, name, and initial value.
2.Follow the data through each expression before considering syntax shortcuts.
3.Compile with warnings enabled; a clean build is part of the result, not an optional polish step.

Watch it run · Build and run

See what this code does

The terminal types this lesson's practice solution and runs it. The scene shows the kind of robot behaviour that code drives. It plays by itself and loops.

Practice code

Now type it yourself

Copy the starter into practice.cpp and replace every TODO with your own code. Build and run it: g++ -std=c++17 -Wall -Wextra -Wpedantic practice.cpp -o practice -pthread && ./practice

#include <iostream>

int main() {
  // TODO: print "standard: " followed by __cplusplus (201703 means C++17)
  return 0;
}

Expected output

standard: 201703

Stuck? Show the full solution (try it yourself first)

#include <iostream>

int main() {
  std::cout << "standard: " << __cplusplus << '\n';
  return 0;
}

Expected result

How you know it worked

After adding the shown fragment to the guided exercise with its listed headers and surrounding program, the finished program builds with -Wall -Wextra -Wpedantic.
Changing the stated input produces the result you predicted.

Practical exercise

Apply the lesson

Write a main.cpp that prints one line. Build it with g++ and with clang++ (if installed) using -std=c++17 -Wall -Wextra -Wpedantic. Add an unused variable, read the warning from each compiler, then remove it.

Before you continue

The program builds with -std=c++17 and no warnings
You can explain the key rule without reading the example
The normal and edge cases both have recorded results

If something goes wrong

The compiler reports that a name or type is unknown.

Start at the first error. Check spelling, required #include lines, and whether the declaration appears before use.

The program runs but the value is wrong.

Print the inputs and intermediate values, then check conversions, units, and collection order.