makefile/script for small program

Question

Hi All,

I have to frequently compile small program and run it. Since, it was tedious to write compile command g++ -W -Wall file.cpp -o out everytime for each cpp file, I wrote one small scripts, which does the compiling.

Here is the script that I wrote

#!/bin/bash
g++ -W -Wall $1 -o $1.out

So, if I have to compile file.cpp, I will do compile file.cpp and it will create file.cpp.out executable for me. And, such file.cpp dont have any header files or any other dependencies.

I know how to write makefile for particular file.cpp like this (very simple case)

file: file.cpp
    g++ -W -Wall file.cpp -o file

but if I have to compile file2.cpp, I have to change above makefile again or write new. So, what I want to do is, when I give make file.cpp command it will produce file as executable. And when I give make file2.cpp it will produce file2 as executable, and similarly for other cpp files.

Answer 1

export CXXFLAGS="-W -Wall"
rm Makefile
make file1

Make has sane defaults. You don't have to write a makefile to use make.

Make has a set of generic rules, which get apply automatically when there is no specific rule. One of them is to make 'file' out of 'file.cpp' using a C++ compiler with flags from environment variable CXXFLAGS. This works a bit like you want...

Answer 2

A Makefile doesn't intend to work as a script; taking particular inputs to generate particular outputs. It, instead, describes dependencies between files, and how to build any dependency, in order to reach a particular target.

Although it is possible to do what you are asking for by creating a target called "file1" and a target called "file2", that's not the idea behind Makefiles; you might be better using a shell script if this is your requirement.

Answer 3

You can have the following target

.cpp:
        g++ -W -Wall [email protected] -o $@

This creates an implicit rule which means that to generate file named x where a file x.cpp already exists, perform the following operation.

When you have the rule, you can just do this from command line:

make file
make file2

Answer 4

%: %.cpp
    g++ -W -Wall $*.cpp -o $*

Answer 5

Simply create a Makefile with the following line

CXXFLAGS=-W -Wall

You can now call e.g.

make foo

and it'll automatically look for a "foo.cpp" file.

Answer 6

Relying on make's default rules for C++, the makefile only needs

CPPFLAGS ?= -W -Wall

Then at the command line:

make file1
make file2
rm file2
make file2 CPPFLAGS="-W -Wall -O3"
rm file2
make file2 CXXFLAGS="-O3"   # possibly a bit too cunning, this one
                            # It has the same effect as the one with CPPFLAGS

Personally, I would add to the makefile

EXECUTABLES = file1 file2

all: $(EXECUTABLES)

clean: 
    rm -f $(EXECUTABLES)

Answer 7

You can run make prog# to build the appropriate program.

CXX=/usr/bin/g++
CXXFLAGS=-W -Wall
TARGETS=prog1 prog2 prog3

all: $(TARGETS)

prog1: prog1.cpp
    $(CXX) $(CXXFLAGS) prog1.cpp -o prog1

prog2: prog2.cpp
    $(CXX) $(CXXFLAGS) prog2.cpp -o prog2

prog3: prog3.cpp
    $(CXX) $(CXXFLAGS) prog3.cpp -o prog3