Shorter and less error-prone rule for automatic prerequisite generation in the GNU Make manual
Hello GNU Make bug-list subscribers On http://www.gnu.org/software/make/manual/make.html#Automatic-Prerequisites The rule for automatically generating prerequisites is %.d: %.c @set -e; rm -f $@; \ $(CC) -M $(CPPFLAGS) $ $...@.; \ sed 's,\($*\)\.o[ :]*,\1.o $@ : ,g' $...@. $@; \ rm -f $...@. but could be replaced with %.d : %.c @$(CC) -MT $@ -MT $*.o -MM $(CPPFLAGS) $ $@ This is simpler. This fixes disagreements about object file names between the sed command and the cc command, should the c file not be found in the current directory. Perhaps it would be time to make this rule part of the default rules in GNU Make? In that case, the -MG option should also be considered for avoiding errors when auto generated headers are included, perhaps via an CCMFLAGS variable. Best regards Robert --- Robert Jørgensgaard Engdahl Cum Laude MSc. C.S. SW-Developer, RD Video Services Applications Bang Olufsen A/S Peter Bangs Vej 15 DK-7600 Struer Denmark Phone: (+45) 96 84 44 05 Internal phone: 454405 e-mail: r...@bang-olufsen.dk Location: Factory 1 - West___ Bug-make mailing list Bug-make@gnu.org http://lists.gnu.org/mailman/listinfo/bug-make
Re: Shorter and less error-prone rule for automatic prerequisite generation in the GNU Make manual
It's also unnecessary - you don't need a rule for %.d at all. You can just generate the dependencies as a side-effect of compilation using -MMD or similar. Well, if a .d file gets deleted while its .o file exists, you do need to regenerate it - or regenerate the .o (which may cause wasteful knock-on actions since it's now newer than it was, even if unchanged). This matters if, for example, you have a make clean-depend rule to purge dependency information. Then use '-include' to grab all the deps if they exist. better: include only the .d files that correspond to .o files *that exist* - if the .o file doesn't exist, you don't need to know what it depends on, aside from the primary source from which it's compiled (which is indicated by the pattern rule that makes the .o file). By providing a rule for the .d files you'll cause make to re-execute itself, so you'll just end up parsing the Makefile twice. Only if you include .d files that aren't really needed (which is common practice). Amendments along these lines are part of the doc-update I keep not finding time to finish up ... Eddy. ___ Bug-make mailing list Bug-make@gnu.org http://lists.gnu.org/mailman/listinfo/bug-make
