GNU make manual 翻译(七十八)

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4.3 Types of Prerequisites                        
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There are actually two different types of prerequisites understood by GNU `make': normal prerequisites such as described in the previous section, and "order-only" prerequisites.  A normal prerequisite makes two statements: first, it imposes an order in which recipes will be invoked: the recipes for all prerequisites of a target will be completed before the recipe for the target is run.  Second, it imposes a dependency relationship: if any prerequisite is newer than the target, then the target is considered out-of-date and must be rebuilt. 
                        
   Normally, this is exactly what you want: if a target's prerequisite 
is updated, then the target should also be updated.                        

4.3 前提条件的类型
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GNU make 可以理解两种不同类型的前提条件:

前面章节中描述的普通的前提条件，以及 仅排序 前提条件。

一个普通的前提条件完成两件事：首先，它确立了一个顺序，片段被激活的时候要运用此顺序:

一个目的的所有前提条件都将被完成后，此目的的片段才会执行。

第二，它确立了一个依赖关系: 如果任何前提条件比目的新，则目的被认为已经过期，需要重新构建。

通常，这正是你所想要的：如果一个前提条件被修改了，那么目的也需要被修改。

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