Compilation process in C - Step-by-Step Execution

Concept Flow - Compilation process in C

Write C source code (.c file)

↓

Preprocessing: handle #include, #define

↓

Compilation: convert to assembly (.s file)

↓

Assembly: convert assembly to machine code (.o file)

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Linking: combine .o files and libraries into executable

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Executable ready

The C compilation process transforms source code step-by-step into an executable program.

Execution Sample

C

#include <stdio.h>
int main() {
  printf("Hi\n");
  return 0;
}

This simple C program prints 'Hi' and returns 0.

Execution Table

Step	Action	Input	Output	Notes
1	Preprocessing	Source code with #include	Expanded code with headers included	Replaces #include and macros
2	Compilation	Preprocessed code	Assembly code (.s file)	Converts C code to assembly instructions
3	Assembly	Assembly code	Object file (.o)	Converts assembly to machine code
4	Linking	Object files + libraries	Executable file	Combines code and libraries into runnable program
5	Execution	Executable file	Program runs and prints output	Program prints 'Hi' to screen
6	Exit	N/A	N/A	Process ends after program finishes

💡 Program finishes execution and returns control to OS

Variable Tracker

Stage	Input Type	Output Type
Preprocessing	Source code (.c)	Expanded source code
Compilation	Expanded source code	Assembly code (.s)
Assembly	Assembly code (.s)	Object file (.o)
Linking	Object files (.o)	Executable file
Execution	Executable file	Program output

Key Moments - 3 Insights

Why does the preprocessor run before compilation?

Because it replaces directives like #include and macros so the compiler gets full code to translate, as shown in execution_table step 1.

What is the difference between assembly and object files?

Assembly files (.s) are human-readable instructions; object files (.o) are machine code, ready for linking, as seen in steps 3 and 4.

Why do we need linking after assembly?

Linking combines multiple object files and libraries into one executable, making the program runnable, shown in step 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output of the compilation step?

A Assembly code (.s file)

B Object file (.o)

C Executable file

D Expanded source code

💡 Hint

Check the 'Compilation' row in execution_table under 'Output' column.

At which step does the program become runnable?

A Preprocessing

B Compilation

C Linking

D Assembly

💡 Hint

Look at the 'Linking' step in execution_table and see what output it produces.

If the #include directive is missing, which step will fail?

A Preprocessing

B Compilation

C Assembly

D Linking

💡 Hint

Refer to key_moments about preprocessing and compilation steps.

Concept Snapshot

C compilation process steps:
1. Preprocessing: expands #includes and macros
2. Compilation: converts code to assembly
3. Assembly: converts assembly to machine code
4. Linking: combines object files into executable
5. Execution: runs the program

Full Transcript

The compilation process in C starts with writing source code. The preprocessor runs first, handling directives like #include and macros, producing expanded code. Then the compiler converts this code into assembly instructions. Next, the assembler turns assembly into machine code stored in object files. The linker combines these object files and libraries into a single executable file. Finally, the executable runs, producing the program output. Each step transforms the code closer to a runnable program.