C-language Multi-file compilation under Linux

If you have more than one source file, there are basically two ways to compile it:
[Suppose there are two source files for TEST.c and TESTFUN.C]

1. Multiple files compile
usage: #gcc testfun.c test.c-o Test
Role: TESTFUN.C and TEST.c are compiled and linked to the test executable file respectively.

2. Compile each source file separately, and then link to the target file after the compiled output.
usage:
#gcc-C testfun.c//TESTFUN.C compiled into TESTFUN.O
#gcc-C test.c//test.c compiled to TEST.O
#gcc-o TESTFUN.O Test.o-o test//TESTFUN.O and TEST.O link to test the

above two methods compare, the first method compiles all the files need to recompile, and the second method can only recompile modified files, unmodified files do not have to recompile.