gcc l option order?

Question

gcc -g -O2 -Wall -I/usr/local/include MyAddressBook.pb-c.c addressbooktest.c -lprotobuf-c -o test

worked, but

gcc -g -O2 -Wall -I/usr/local/include -lprotobuf-c -o addressbooktest addressbooktest.c MyAddressBook.pb-c.c

didn't.

man gcc said that

For the most part, the order you use doesn't matter. Order does matter when you use several options of the same kind; for example, if you specify -L more than once, the directories are searched in the order specified. Also, the placement of the -l option is significant.

however I cannot understand how the use of -L and -l option change compile logic.

How can I know where to use -L, -l option?

score 0 · Accepted Answer · answered Jan 25 '22 at 06:42

When you use

gcc -g -O2 -Wall -I/usr/local/include -lprotobuf-c -o addressbooktest addressbooktest.c MyAddressBook.pb-c.c

the linker (which is a separate program which is invoked by the gcc front-end program) runs, it will find the library protobuf-c but since no one (yet) uses any functions from it, it will be ignored.

gcc l option order?

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