.c and .o files

• we learnt about .c and .h files, so what are .o files ??
• .o file means object file, Contains the compiled contents of the corresponding .c program, compiled as in assembly form.
• Lets take example of 01, command to compile was gcc main.c library.c, this was as we need to combine function in library.c and main.c for the program to run, if we only compile main.c, there’s only declaration of welcome_user, but a definiton is missing, i.e. compiler doesnot know what it needs to do when welcome_user function is called. So we need to link these to files together. gcc main.c library.c automatically does that for us.

• Other way to do this is compile the respective .c files in its object file and then link them together.

• Example: gcc -c main.c you will see a main.o file, it contains compiled contents of main.c, open it you will see gibberish
• gcc -c library.c you will see library.o file, again gibberish
• Now, these two .o files contain functions compiled in binary form, we need them to link together for them to work so we link them. we call this process linking
• gcc -o main main.o library.o now we can see we passed both the .o files to the compiler, it merged them and formed a single binary, same process take place even for 1000s of files.