How to ensure a target is run before all the other build rules in a makefile?

Question

I have a C++ project which contains a generated file that all the other C++ files depend on. I\'m trying to force that file to be generated and compiled before any other com

Answer 1

If you're sure that's really what you want, here's one way to do it: have a rule for a dummy file which the makefile will include.

.PHONY: dummy
dummy:
    # generate the file here

-include dummy

No matter what target you specify, Make will first run the dummy rule, then restart itself.

Answer 2

Actually, other cpp files don't depend on the generated one (in terms of Make rules). Dependency graph still looks like:

program
 |
 ^- file1.o
 |   ^- file1.c
 |
 ^- file2.o
 |   ^- file2.c
 |
 ^- generated_file.o
     ^- generated_file.c
         ^- <generator prerequisites>

Your source files could only depend on some kind of generated header file (in case when it is #included by these sources).

If you need to generate only a cpp file then the following makefile should be sufficient:

srcs := $(wildcard src/*.cpp src/*/*.cpp)

gen_file := gen/generated_file.cpp
srcs += $(gen_file)

objs := $(srcs:.cpp=.o)

.PHONY : all
all : program

program : $(objs)
    @$(LD) ...

%.o : %.c
    @$(CC) ...

$(gen_file) :
    # generate the file here

UPD.

A little improvement based on Beta's answer.

-include generator-task
.PHONY : generator-task

generator-task : $(gen_files)

$(gen_files) : $(gen_prerequisites)
    # generate the file here

Instead of running generator on each invocation of Make, this will only regenerate a file when one of its prerequisites would change.