C++ Compilation process

The process of converting human-readable C++ code into an executable machine program involves multiple stages. Each stage plays a critical role in ensuring that our code runs as intended.

We'll walk through the entire C++ compilation process, step-by-step, from source code to executable.

Steps involved in Compilation:

1. Source Code (.cpp, .h files)
2. Preprocessing
3. Compilation
4. Assembly
5. Linking
6. Execution

1. Source Code

Source code is the C++ code that the programmer writes. It usually consists of:

• .cpp files: contain function definitions and main()
• .h files: contain function declarations or constants (headers)

Example:

Note: In the above example, math_utils.h is assumed to be a user-defined header file that contains the declaration (and corresponding definition in a separate .cpp file) of the add() function. It is not part of the C++ standard library and must be created separately for the program to compile successfully.

2. Preprocessing

The preprocessor handles lines that start with # (like #include, #define, etc.) and prepares the code for the compiler. It:

• Replaces #include <....> with actual code from the included files.
• Expands macros
• Handles conditional compilation (#ifdef, etc.)

Command:

g++ -E main.cpp -o main.i

Output: The output (main.i) contains pure C++ code with all header files inserted and macros expanded.

Example:

3. Compilation

The compiler translates preprocessed C++ code into assembly language, which is human readable low-level code, It :

• Does Syntax checking
• Converts C++ to Assembly code (.s file)

Command:

g++ -S main.i -o main.s

Output: main.s contains low-level assembly instructions.

Example: C++

Assembly:

4. Assembly

The assembler converts the assembly code into object code, which is machine-readable binary (.o file).

Command:

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

Output: A .o (object file) that contains machine code, not yet executable on its own

5. Linking

The linker combines multiple object files (main.o, math_utils.o) and links in external libraries (like iostream), creating a final executable. It:

• Connects the main() function in main.o to add() in math_utils.o
• Resolves symbols from the standard library

Command:

g++ main.o math_utils.o -o main

Output

An executable file (usually called main or whatever name you give)

6. Execution

It is the final executable produced by the linker.

Command

./main

Output

Result: 15

Tools Involved in the Compilation Pipeline

Common Errors at Each Stage