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.
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:.c
files, then it will be newer thanhello
, and then it will have to rebuild when you run make.hello
, then it will obviously have to rebuild it-B
option.make -B all
make clean all
will deletehello
and require a rebuild. (I suggest you look at @Mat's comment aboutrm -f *.o hello
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.
Remove the
hello
file from your folder and try again.The
all
target depends on thehello
target. Thehello
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.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.
instead of
Please see the GNU make manual for the rule syntax description: https://www.gnu.org/software/make/manual/make.html#Rule-Syntax
That is not an error the make command in unix works based on the timestamps,i.e lets say if you have made certain changes to factorial.cpp and compile using make..then make shows the informarion 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 then 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 make file 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......
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!