GNU make manual 翻译(七十四)

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4.1 Rule Example                       
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Here is an example of a rule: 
     foo.o : foo.c defs.h       # module for twiddling the frobs                                     cc -c -g foo.c                        
                        
   Its target is `foo.o' and its prerequisites are `foo.c' and  `defs.h'.  It has one command in the recipe: `cc -c -g foo.c'.  The recipe starts with a tab to identify it as a recipe.                        
                        
   This rule says two things:                        
                        
   * How to decide whether `foo.o' is out of date: it is out of date if it does not exist, or if either `foo.c' or `defs.h' is more recent than it.  
                        
   * How to update the file `foo.o': by running `cc' as stated.  The recipe does not explicitly mention `defs.h', but we presume that `foo.c' includes it, and that that is why `defs.h' was added to the prerequisites.                        

4.1 规则例子

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这里有一个规则的例子：

foo.o : foo.c defs.h # module for twiddling the frobs
　　cc -c -g foo.c
目标是 foo.o， 它的前提条件是 foo.c 和 defs.h。它的片段拥有一个命令行：

cc -c -g foo.c 片段行开头有一个tab 符号，表明其为片段。

此规则说了两件事情：

*如何判定，是否 foo.o已经过期：如果它不存在，或者 foo.c 或 defs.h 比它新。

*如何通过运行 片段中声明的 cc命令来更改 foo.o 文件。此片段没有显式地提及 defs.h， 但是我们假设foo.c 包含了它，这也是 defs.h 出现在 前提条件中的原因。

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