Compiler

Once the preprocessor has finished, the "compiler" takes over. The compiler reads your (now expanded) C++ code and translates it into "object code" — machine instructions specific to your computer's processor. Common C++ compilers include g++ (GCC), clang++, and Microsoft's MSVC.

Unlike some other languages, the C++ compiler translates your code straight toward native machine instructions for your specific processor and operating system — not into some universal, platform-independent middle format. This is one reason C++ programs can run so fast: there is no extra translation step left to do once compiling is done.

g++ -c main.cpp -o main.o

The C++ compiler translates source code into ____ code, made up of native machine instructions.

The output of the compiler is stored in an "object file" (extension ".o" on Linux/macOS, ".obj" on Windows). Importantly, an object file on its own usually is not yet a runnable program — especially if your code calls functions defined elsewhere, like printing text to the screen, which live in the standard library.

The compiler also checks your code for errors along the way. If you misspell a keyword, forget a semicolon, or use a variable incorrectly, the compiler stops and reports a "compile error" — no object file is produced until the mistake is fixed.

What happens if your C++ source code contains a mistake, like a missing semicolon?

An object file produced by the compiler is always immediately runnable on its own.