Everything you have to know about libraries in C

2 min readMar 7, 2021

Prerequisites:

The biggest problem with the C language is that at one point, the program grows so big that a file is not enough to store the functions.

To resolve that, fortunately for us, we have libraries.

It exists two types of libraries: Static and Dynamic.

Begin by the static one.

Step 1: Create object files

gcc -c fileName.c

This command compile fileName.c in object file and name it as fileName.o.

Step 2: Create static library from object files

ar rc lib.a fileName.o

To generate a static library, you have to create an archive with object files.

c option: to create an archive.

r option: to replace older file with new one.

Step 3: Create an index

ranlib lib.

ranlib makes a header in the library with the symbols of the object file contents.This helps the compiler to quickly reference symbols.

Step 4: Generate your library

gcc -L. main.c -llib -o main.out

L option: specifies the path of the library

l option: specifies the library to use (you don’t have to specify the extension)

You can now execute the program.

./main.out

And now, dynamic!

Step 1: Create object file

gcc -fPIC -c fileName.c -o dynFileName.o

f option: PIC makes position independent code

Step 2: Convert object file to dynamic object file

gcc -shared -o dynFileName.so

share option:

Step 3: Create a dynamic library

gcc -o fileName.c dynFileName.so