一、make/Makefile是什么？
简单来说，make是一条命令，Makefile是一个文件，两个搭配使用，完成项目自动化构建。 详解： 一个工程中的源文件不计其数，其按类型、功能、模块分别放在若干个目录中，makefile定义了一系列的规则来指定，哪些文件需要先编译，哪些文件需要后编译，哪些文件需要重新编译，甚至于进行更复杂的功能操作。 makefile带来的好处就是⸺“自动化编译”，一旦写好，只需要一个make命令，整个工程完全自动编译，极大的提高了软件开发的效率。 make是一个命令工具，是一个解释makefile中指令的命令工具。
二、make/Makefile的基本概念
首先，建立一个Makefile文件
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touch Makefile # Makefile/makefile都可以，我们习惯于Makefile然后，保证你有个mypro.c的c文件，然后对Makefile写入：
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mypro:mypro.c gcc mypro.c -o mypro # 前面的空格是一个tab的结果依赖关系和依赖方法说明
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即mypro依赖于mypro.c，而gcc myproc.c -o myproc 正是这种依赖方法。
在对Makefile写入上述依赖关系与依赖方法之后，我们就可以直接使用make命令了。
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上面我们只是完成了Makefile的冰山一角，有个基础的认识。 我们可以用Makefile快速生成可执行，那有没有快速清理项目的呢？
项目清理
我们可以在已经有的Makefile再进行增加：
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mypro:mypro.c gcc mypro.c -o mypro .PHONY:clean clean: # 可以没有依赖关系 rm -f myproc有了上面的Makefile，我们就可以进行项目清理了： 像clean这种，没有被第一个目标文件直接或间接关联，那么它后面所定义的命令将不会被自动执行，不过，我们可以显示要make执行。即命令⸺make clean，以此来清除所有的目标文件，以便重编译。
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.PHONY **但是一般我们这种clean的目标问文件，我们将它设置为伪目标，用.PHONY修饰，伪目标的特性是总是被执行的**。 我们也可以对第一组依赖关系用.PHONY修饰，来看看效果： 未修饰之前：
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修饰之后：
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有这些理解，我们来看看什么叫做总是被执行？
什么叫做总是被执行？
我们要知道，在编译的时候，默认老代码（以前编译过）是不会别重新编译的，很好理解，但是编译器是如何知道你是老代码还是新代码/更改过的代码。
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