Improve this answer. Simon Simon 2, 1 1 gold badge 11 11 silver badges 14 14 bronze badges. Does it mean that KDIR is already declared somewhere in the system? It doesn't have to be, since? Simon Note that command line arguments to make already override Makefile variables without the need of? Thanks to Simon and R.
Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. We can override this behavior using a special phony target called. As the name suggests, the phony target. This is why most makefiles include all as a target that can call as many targets as needed. Before running make , let's include another special phony target,.
PHONY , where we define all the targets that are not files. Here is the complete makefile:. It is a good practice not to call clean in all or put it as the first target. Now that you have an idea of how a basic makefile works and how to write a simple makefile, let's look at some more advanced examples.
Our latest Linux articles In the above example, most target and prerequisite values are hard-coded, but in real projects, these are replaced with variables and patterns. For example, to assign the command gcc to a variable CC :. This is also called a recursive expanded variable , and it is used in a rule as shown below:. But if one tries to reassign a variable to itself, it will cause an infinite loop. Let's verify this:. We should have no problem running the makefile below:. The following makefile can compile all C programs by using variables, patterns, and functions.
Let's explore it line by line:. In this case, all files with the. In this case, if SRCS has values 'foo. Let's look at an example to understand this rule. Below is the rule in its expanded form:. Every prerequisite in the previous rule is considered a target for this rule. Below is the rewrite of the above makefile, assuming it is placed in the directory having a single file foo.
For more on makefiles, refer to the GNU Make manual , which offers a complete reference and examples. You can also read our Introduction to GNU Autotools to learn how to automate the generation of a makefile for your coding project.
What is a Makefile and how does it work? Run and compile your programs more efficiently with this handy automation tool. Image by :. Get the highlights in your inbox every week. There are some makefiles to test. The first one, mkfile1 :. There is a point to be understood here. So, why main. The make command processed main.
So, the suffix rule. That means name of current dependency. In the case of. There are others:. Now it only renames file. The keyword.
In case of mkfile2 , they are. Some extensions like. The suffix rule. It works as if file. So far we saw how to define suffix rules but we did not use them in a real situation.
So, let us move to a more realistic scenario by using the C source code in the sample4 directory. Let us try the following sequence of commands Figure 9 :.
What went wrong at item 7? You can edit and add the last three lines and try the sequence of commands of figure 9 again. Do not forget to remove objects before testing it again:. Well, add the dependencies for each module indicating the exact include file each one includes is good but not practical. Imagine your project with That is a lot of typing! I did mkfile4 that way because it is more practical and that does not mean there is any error. You can separate headers by module if you want.
Tip : When working on big projects I used to put only master header files as dependency. That means, those headers that are included by all or most modules. When you are working in a large project with many different parts such as libraries, DLLs, executables, it is a good idea to split them in a directory structure by keeping the source of each module in its own directory.
Thus, each source directory might have its own makefile and it can be called by a master makefile. The master makefile is kept into root directory and it changes into each sub-directory to invoke the module's makefile. It sounds simple and it really is. But there is a trick you should know when you force the make command to change into other directory. For instance, let us test the simple makefile :. The pwd command prints the current directory.
What that means? You should know that most shell commands like cp , mv and so on force make command:. In fact, make creates three different instances of shell to process each of those commands. The brackets ensure that all commands are processed by a single shell - make command starts only one shell to execute all three commands. So, you can imagine what would happen when you do not use brackets and your makefile was:. You see what happens when you try it without brackets?
It is calling the same makefile recursively. For instance, make[37] means the 37th instance of make command.
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