On Tue, 2021-03-30 at 11:47 -0500, Peng Yu wrote: > Hi, > > crypt(3) does not need -lcrypt on macOS, but need -lcrypt on Linux. > How does autoconf determine what library needs to be linked based on > the source code? Thanks. > AC_SEARCH_LIBS doesn't use the source code; instead it tries to link a test program -- first with no libraries at all, and then with each of the libraries you've suggested to it, in succession. So on macOS, it would succeed without -lcrypt immediately. On linux, the first attempt would fail, but the second attempt with -lcrypt would succeed. The necessary -l<library> flags are then prepended to the $LIBS variable for use in the build system.
