Compilation Process for C programs with GCC

compilation_process.md

Compilation Process for C programs with GCC

• C is a programming language.
• Programs written in C end with a .c extension.
• .c files are human-readable, written in plain text using alphanumeric and math symbols
• This makes C is a high-level language.
• Computer hardware, on the other hand, communicate using low-level languages.
  • Low-level languages can either be Machine language or Assembly language.
  • Machine language is in binary, ones and zeros.
  • Assembly language is written with a set of letters and symbols.
• It is necessary to convert .c files to a language the computer hardware can understand.
• Compilers do this conversion. From source language to target language.
• A very popular compiler is the GCC. GNU Compiler Collection.

Compilation Process

• The compilation process involves the following steps.
  • Preprocessing
  • Compilation
  • Assemble
  • Linking
• Here's the basic structure of a command to compile a C program in linux.

seg@fault: gcc -[options] [filename]

• As an example, let's create a simple C program called main.c.

seg@fault: touch main.c
seg@fault: ls
main.c

• The code contained in main.c looks like this.

#include <stdio.h>

/**
 * main - entry point of the program. Prints "Hello World" in the terminal
 *
 * Return: Always 0. (Success)
*/
int main()
{
	printf("Hello World.\n");

	return (0);
}

• To compile the main.c file, run the gcc main.c command.
• This will create a file called a.out which is an executable file.

seg@fault: gcc main.c
seg@fault: ls
main.c a.out

• To run the executable file a.out. Write the following command.

seg@fault: ./a.out
Hello World
seg@fault:

• The compilation process above went through the following steps; preprocessing, compile, assembly, linking.

Preprocessing Step

• In the preprocessing step, the preprocessor;
  • removes all the comments in the C file.
  • searches for and includes the code of the files referred to with #include statements to a file that will go to the next step of the process.
  • replaces the content of tokens from #define statements with the defined values.
• To generate preprocessor files to a file called preprocessor using gcc on linux, use the following command. Note the -E flag passed as an option.

seg@fault: gcc -E main.c > preprocessor

Compile Step

• In the compile step;
  • the output file from the preprocessing step is translated to assembly code.
  • the resulting file from this step has a .s extension.
• Something to note, this is the step that actually generates assembly code. It may be elusively thought that the assemble stage generates assembly code.
• To generate assembly code using gcc on linux, use the following command.

seg@fault: gcc -S main.c

Assemble Step

• In the assemble step;
  • The assembly code generated from the previous step is converted to machine code.
  • The machine code generated from this step is an object file that and has a .o extension.
• To generate machine code using gcc on linux, use the following command.

seg@fault: gcc -c main.c

Linking Step

• This is the final step in the process.
• This process links all the files generated from previous steps into one.
• The executable file is the output from this step.