make Nothing to be done for all

Question

I am going through an eg pgm to create a make file   http   mrbook org tutorials make   My folder eg make creation contains the following files   desktop   eg make creation  ls factorial c  functions h  hello  hello c  main c  Makefile   Makefile    I am a comment  and I want to say that the variable CC will be   the compiler to use  CC gcc   Hwy   I am comment no 2  I want to say that CFLAGS will be the  options I ll pass to the compiler CFLAGS -c -Wall  all hello  hello main o factorial o hello o     CC  main o factorial o hello o -o hello  main o main c     CC    CFLAGS  main c  factorial o factorial c     CC    CFLAGS  factorial c  hello o hello c     CC    CFLAGS  hello c  clean    rm -rf  o hello   error   desktop   eg make creation  make all make  Nothing to be done for  all     Please help me understand to compile this program

User · Answer

That is not an error  the make command in unix works based on the timestamps  I e let s say if you have made certain changes to factorial cpp and compile using make then make shows the information that only the cc -o factorial cpp command is executed  Next time if you execute the same command i e make without making any changes to any file with  cpp extension the compiler says that the output file is up to date  The compiler gives this information until we make certain changes to any file cpp  The advantage of the makefile is that it reduces the recompiling time by compiling the only files that are modified and by using the object   o  files  of the unmodified files directly

User · Answer

Sometimes  Nothing to be done for all  error can be caused by spaces before command in makefile rule instead of tab  Please ensure that you use tabs instead of spaces inside of your rules   all   lt  t gt   CC    CFLAGS        instead of  all        CC    CFLAGS        Please see the GNU make manual for the rule syntax description  https   www gnu org software make manual make html Rule-Syntax

User · Answer

I think you missed a tab in 9th line  The line following all hello must be a blank tab  Make sure that you have a blank tab in 9th line  It will make the interpreter understand that you want to use default recipe for makefile

User · Answer

Remove the hello file from your folder and try again   The all target depends on the hello target  The hello target first tries to find the corresponding file in the filesystem  If it finds it and it is up to date with the dependent files   there is nothing to do

User · Answer

When you just give make  it makes the first rule in your makefile  i e  all   You have specified that  all  depends on  hello   which depends on main o  factorial o and hello o  So  make  tries to see if those files are present   If they are present   make  sees if their dependencies  e g  main o has a dependency main c  have changed  If they have changed  make rebuilds them  else skips the rule  Similarly it recursively goes on building the files that have changed and finally runs the top most command   all  in your case to give you a executable   hello  in your case   If they are not present  make blindly builds everything under the rule   Coming to your problem  it isn t an error but  make  is saying that every dependency in your makefile is up to date and it doesn t need to make anything

User · Answer

Make is behaving correctly  hello already exists and is not older than the  c files  and therefore there is no more work to be done  There are four scenarios in which make will need to  re build    If you modify one of your  c files  then it will be newer than hello  and then it will have to rebuild when you run make  If you delete hello  then it will obviously have to rebuild it You can force make to rebuild everything with the -B option  make -B all make clean all will delete hello and require a rebuild   I suggest you look at  Mat s comment about rm -f   o hello

User · Answer

I arrived at this peculiar  hard-to-debug error through a different route  My trouble ended up being that I was using a pattern rule in a build step when the target and the dependency were located in distinct directories  Something like this   foo apple o  bar apple c   FOODEPS     o    c       CC    lt  -o      I had several dependencies set up this way  and was trying to use one pattern recipe for them all  Clearly  a single substitution for     isn t going to work here  I made explicit rules for each dependency  and I found myself back among the puppies and unicorns   foo apple o  bar apple c   FOODEPS        CC    lt  -o      Hope this helps someone

[c] make: Nothing to be done for `all'

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