I have a final exam next week, and in the exercise paper which is given us to study, there is a gcc option that I could not find on gcc manual page.

It is something like that gcc -J 4 program.c -o filename.

Is there someone knows that what it is for?

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    Sorry but it's borderline stupid to ask you to use an undocumented option if it's not covered in your course manual. – Julie Pelletier Jun 3 '16 at 22:08
  • gcc will complain with a lower case j : -j 4 : unrecognized command line option ‘-j’ . gcc: error: 4: No such file or directory. ... But is OK with -J 4 , i.e. an upper case J. - – Knud Larsen Jun 3 '16 at 23:10
  • @JuliePelletier I bet is an old gcc version – Braiam Jun 3 '16 at 23:31
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    I tried skimming the sources at github github.com/gcc-mirror/gcc/blob/master/gcc/opts-global.c and the online documentation gcc.gnu.org/onlinedocs. Nowhere is documented. Gfortran has a -J defined gcc.gnu.org/onlinedocs/gfortran/Directory-Options.html – Braiam Jun 3 '16 at 23:49
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    Since you wrote -J 4, as in with a number, and, since it doesn't seem to match anything in gcc, I wonder if this is confused with the -j <N>option of make. In make, it sets the maximum number of compilations to run in parallel: on a four-processor system one might run make -j4 to utilize all processors. – ilkkachu Jun 4 '16 at 10:04

There's only a Gfortran specific option called -J, but this doesn't make sense combined with a number. Other alternative is that is being confused with make -j n flag that determines the maximum number of concurrent compilation process.

  • Hi, what's the default if -j isn't specified? Thanks! – Hei Jan 3 '18 at 5:17

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