C makefile example
GNU make also supports automatic variables that take special values whenĮvaluated in a command script. Specified in the makefile itself take precedence over values specified on the command Values specified on theĬommand line take precedence over values inherited from the environment values Starts up, each environment variable is used to initialize a make variable with the same name and value. You can also set the value of a make variable on the command line, using the syntax See, make variables can be assigned values using the assignment operator =, and they can be evaluated by enclosing them in Here I’ve introduced two make variables, OUTPUTFILE and INSTALLDIR. # Copy hello to the binaries subdirectory
#C makefile example install#
# Specify the target file and the install directory Similarly, make clean invokes the command rm -f hello If it doesn’t already exist the second command copies hello The first command creates the directory binaries, Therefore executing make install causes the following commands to be When you invoke make with a command-line argument corresponding to a target, makeĪttempts to build that target. So make builds the all target - by executing an empty command script - and exits.
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The prerequisite to the all target is now up to date, Consequently, make invokes g++ to compile and link hello.cpp, producing the file hello. However, because the file hello.cpp exists, andīecause hello.cpp does not appear as the target of any Assuming that the current directory isĮmpty except for makefile and hello.cpp, the target hello is not up to date. With target hello tells make to build hello, if necessary, by The all target may have several prerequisites. No need for an all target in more complex examples, The phony target all is always out of date: its only purpose is to tell make toīuild hello.exe. Now let’s look at what happens when we execute the makefile in Example 1-14. Provided it doesn’t appear as the target of a rule. PHONY attribute, as in Example 1-14 and Example 1-15, you can tell make that the target does not correspond to a file, and soĬonversely, a prerequisite corresponding to an existing file is always up to date, Such targets are called phony targets.īy labeling a target with the. Therefore, a targetĬorresponding to a non-existent file is never up to date, and can be used to force aĬommand script to be executed unconditionally. It follows from the above description that a target having no prerequisites is up toĭate if and only if it corresponds to a file on the filesystem. The default target is up to date or until an error occurs.
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That prerequisite as a target, and starts the whole process again. Is not up to date, make searches for a rule having Up to date, this process is recursive: for each prerequisite which Otherwise, it attempts to generate the default targetįrom its prerequisites by executing its command script. Prerequisites has been modified more recently than it has.
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That it exists, that all its prerequisites are up to date, and that none of its If the default target is up to date - meaning When make is invoked with no arguments, it looks in the currentĭirectory for a file named GNUmakefile, makefile or Makefile,Īnd attempts to build the first target it contains, called the default But what does it actually do? Here’s how it works. In the next few recipes, you’ll see that GNU make is a powerful tool for buildingĬomplex projects.
#C makefile example code#
Phony targets, using the PHONY attribute.įor example, to build an executable from the source code in Example 1-4 using GCC, your makefile might The clean and install targets should both be labeled as Its command script should remove the executable and the intermediate objectįile from the current directory. Prerequisites, and should have a command script to copy the executable from the directoryĬontaining the makefile to the directory where you want it installed. Specify yourĪpplication’s source file as its prerequisite, and specify the command line needed toīuild the executable from the source file as your target’s command script. Give the second target the same name as your executable. The name of the executable you wish to build as its sole prerequisite. Create a text file named makefile in the directory containing your source file. In the following examples, lines which begin with a Tab are indicated by an With a Tab rather than a Space - this is a source of some of the most common beginnerĮrrors. Lines containing command scripts must begin