What happens when you type gcc main.c
Jhon Edison Arias Esparza
Fullstack Developer at Ceiba Software with expertise in Java, Node.js, and AWS
The GNU Compiler Collection (GCC) is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain and the standard compiler for most projects related to GNU and Linux, including the Linux kernel. The Free Software Foundation (FSF) distributes GCC under the GNU General Public License General Public License (GNU GPL). GCC has played an important role in the growth of free software, as both a tool and an example.
But What happens when you type gcc main.c, it is divided into 4 things.
- Preprocessing
- Compiling
- Assembling
- Linking
Preprocessing.
Preprocessing is the first step. The preprocessor obeys commands that begin with # (known as directives) by:
- removing comments
- expanding macros
- expanding included files
If you included a header file such as #include <stdio.h>, it will look for the stdio.h file and copy the header file into the source code file.
The preprocessor also generates macro code and replaces symbolic constants defined using #define with their values.
Compiling
Compiling is the second step. It takes the output of the preprocessor and generates assembly language, an intermediate human readable language, specific to the target processor.
Assembling
Assembly is the third step of compilation. The assembler will convert the assembly code into pure binary code or machine code (zeros and ones). This code is also known as object code.
Linking
Linking is the final step of compilation. The linker merges all the object code from multiple modules into a single one. If we are using a function from libraries, linker will link our code with that library function code.
In static linking, the linker makes a copy of all used library functions to the executable file. In dynamic linking, the code is not copied, it is done by just placing the name of the library in the binary file.