![]() # Rule repository, note that it's recommended to use a pinned commit to a released version of the rules The contents of the workspace file are: workspace(name = "http_archive") I created the Build folder where i will be putting the build files. The folder structure looks like this:īazelCmake is the parent folder and Source subfolder contains the source files. all: f1.o f2.oĮcho # Equivalent to: # f1.o: # echo f1.o # f2.o: # echo f2.o Automatic Variables and Wildcards * Wildcardīoth * and % are called wildcards in Make, but they mean entirely different things.I am trying to build a CMake project using Bazel. is an automatic variable that contains the target name. When there are multiple targets for a rule, the commands will be run for each target. Since this is the first rule listed, it will run by default if make is called without specifying a target. Making multiple targets and you want all of them to run? Make an all target. But before we do, make a file called blah.c that has the following contents: // blah.c int main () or $() x := dude Let's create a more typical Makefile - one that compiles a single C file. In this case, the hello target does not create the hello file. Typically, when a target is run (aka when the commands of a target are run), the commands will create a file with the same name as the target. ![]() That's because the two are directly tied together. It's important to realize that I'm talking about hello as both a target and a file. If hello does exist, no commands will run. As long as the hello file does not exist, the commands will run. Let's start with a hello world example: hello:Įcho "This line will always print, because the file hello does not exist." These files need to exist before the commands for the target are run. The prerequisites are also file names, separated by spaces.These need to start with a tab character, not spaces. The commands are a series of steps typically used to make the target(s).The targets are file names, separated by spaces.A rule generally looks like this: targets: prerequisites That's it! If you're a bit confused, here's a video that goes through these steps, along with describing the basic structure of Makefiles.Ī Makefile consists of a set of rules. Here is the output of running the above example: $ make Note: Makefiles must be indented using TABs and not spaces or make will fail. Let's start with the simplest of Makefiles: hello: For each example, put the contents in a file called Makefile, and in that directory run the command make. To run these examples, you'll need a terminal and "make" installed. All the examples work for Make versions 3 and 4, which are nearly equivalent other than some esoteric differences. However, it's specifically written for GNU Make, which is the standard implementation on Linux and MacOS. There are a variety of implementations of Make, but most of this guide will work on whatever version you're using. When the program runs, the most recent version of the file is used. But when files in interpreted languages change, nothing needs to get recompiled. The goal of Makefiles is to compile whatever files need to be compiled, based on what files have changed. Interpreted languages like Python, Ruby, and Javascript don't require an analogue to Makefiles. Other languages like Go and Rust have their own build tools. For Java, there's Ant, Maven, and Gradle. Some code editors like Microsoft Visual Studio have their own built in build tools. Popular C/C++ alternative build systems are SCons, CMake, Bazel, and Ninja. If any file's dependencies changes, then the file will get recompiled: Here's an example dependency graph that you might build with Make. ![]() ![]() This tutorial will focus on the C/C++ compilation use case. Make can also be used beyond compilation too, when you need a series of instructions to run depending on what files have changed. ![]() Other languages typically have their own tools that serve a similar purpose as Make. In the vast majority of cases, C or C++ files are compiled. Makefiles are used to help decide which parts of a large program need to be recompiled. Good luck, and I hope you are able to slay the confusing world of Makefiles! Getting Started Why do Makefiles exist? If you mostly understand Make, consider checking out the Makefile Cookbook, which has a template for medium sized projects with ample comments about what each part of the Makefile is doing. Each topic has a brief description and a self contained example that you can run yourself. I've condensed the most critical knowledge into this guide. To solve this, I sat down for several weekends and read everything I could about Makefiles. They seemed awash with hidden rules and esoteric symbols, and asking simple questions didn’t yield simple answers. I built this guide because I could never quite wrap my head around Makefiles. ![]()
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