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Thinking in C++
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Make activities

When you type make (or whatever the name of your “make” program happens to be), the make program looks in the current directory for a file named makefile, which you’ve created if it’s your project. This file lists dependencies between source code files. make looks at the dates on files. If a dependent file has an older date than a file it depends on, make executes the rule given after the dependency.

All comments in makefiles start with a # and continue to the end of the line.

As a simple example, the makefile for a program called “hello” might contain:

# A comment
hello.exe: hello.cpp
        mycompiler hello.cpp

This says that hello.exe (the target) depends on hello.cpp. When hello.cpp has a newer date than hello.exe, make executes the “rule” mycompiler hello.cpp. There may be multiple dependencies and multiple rules. Many make programs require that all the rules begin with a tab. Other than that, whitespace is generally ignored so you can format for readability.

The rules are not restricted to being calls to the compiler; you can call any program you want from within make. By creating groups of interdependent dependency-rule sets, you can modify your source code files, type make and be certain that all the affected files will be rebuilt correctly.

Thinking in C++
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire