Whenever we create a file with custom function definitions, say utils.c and its corresponding header file utils.h containing the function declarations. I have to compile the utils.c file along with the driver code that I am using it in, with a command like gcc driver.c utils.c -o my_exe.
So what instruction compiles the standard C files, whose header files we include like stdio.h?
Compiling is a three step process. Preprocessing, Compilation and Linking.
gcc driver.c utils.c -o my_exe is short hand for:
gcc -c driver.c -o driver.o
gcc -c utils.c -o utils.o
ld driver.o utils.o -o my_exe
Which is compile driver, compile utils and then link everything together.
Recompilation is still missing in our example. The includes is copied into the c files for compilation. The following steps breaks it up even further to show the preprocessing that handles the code in the header files:
gcc -E driver.c -o driver.i
gcc driver.i -o driver.o
gcc -E utils.c > utils.i
gcc utils.i -o utils.o
ld driver.o utils.o -o my_exe
gcc driver.o utils.o -o my_exe can also be changed include libraries with for example -lm to include standard math library (libm.a or libm.so). Libraries is just precompiled c source code (object code or .o) in a container file.
The standard libraries (as in stdlib.h and stdio.h) is libc.so (or libc.a). You do not need to link them in explicitly but you can if you want to.
Then gcc driver.o utils.o -o my_exe becomes gcc driver.o utils.o -o my_exe -lc
You can precompile your code in the same manner for later linking:
gcc -c utils.c -o utils.o
ar rcs libUtils.a utils.o
gcc driver.c -L. -lUtils -o my_exe