We can also compile each C file separately using the cc -c option. This produces an object file with the same name, but ending in .o. After this, the object files are linked using the linker. This would require the four following commands for our current example.
cc -c prog.c cc -c func1.c cc -c func2.c ld prog.o func1.o func2.o -o prog
Each file is compiled before the object files are linked to give a runnable file.
The advantage of separate compilation is that only files which have been edited since the last compilation need to be re-compiled when re-building the program. For very large programs this can save a lot of time.
The make utility is designed to automate this re-building process. It checks the times of modification of files, and selectively re-compiles as required. It is an excellent tool for maintaining multi-file programs. Its use is recommended when building multi-file programs.
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