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cmakefile

Why does the gnu make command default to compiling c files with the same name

environment

os: macos 12.6.3 (intel)

gnu make: 3.81

execute command: make -v get:

GNU Make 3.81
Copyright (C) 2006  Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
 
This program built for i386-apple-darwin11.3.0

steps

The directory structure is as follows

./
├── Makefile
└── abc.c

There are only two files in the directory: Makefile and abc.c, where the abc.c file is empty file and has no content

The content of the Makefile is as follows:

test: abc.o
    @echo 'execute test.'
clean:
    $(RM) test abc.o
.PHONY: test clean

Then, execute command: make clean && make test , It will output:

rm -f test abc.o
cc    -c -o abc.o abc.c
execute test.

So, My question is, why does the make command automatically execute the cc -c -o command in the second line of output? Is this make command default behavior?

I tried renaming the abc.c file to abc.java and executing the command again, which was output as I expected. My original intention was to check if the abc.o file exists, if file not exist, throw an error or output something

I cannot simply describe this issue, so I don't know how to use Google search. Can you provide me with an official document link to explain this behavior, or are there parameters that can avoid this default behavior?

Solution

  • make has implicit rule that will compile a .c file into a .o file. For more details take a look at the make manual here: https://www.gnu.org/software/make/manual/make.html#Implicit-Rules

    The --no-builtin-rules flag will prevent this behaviour.