10. Writing rules - Document Search

1. VPATH

In some big projects , There are a lot of source files , Our usual practice is to classify these many source files , And stored in different directories . therefore , When make When you need to find the dependency of a file , You can put a path in front of the file , But the best way is to give a path to make, Give Way make It's automatically looking for .
Makefile Special variables in the file “VPATH” That's how it works , If this variable is not specified ,make Only look for dependent and target files in the current directory . If you define this variable , that ,make When the current directory cannot be found , Found the specified directory .

VPATH = src:../headers

The above definition specifies two directories ,“src” and “…/headers”,make Search in this order . The catalogue is made up of “ The colon :” Separate .（ Of course , The current directory is always the highest priority search place ）

2. vpath

Another way to set the file search path is to use make Of “vpath” keyword （ Be careful , It's all lowercase ）, This is not a variable , This is a make Key words of , This and the one mentioned above VPATH Variables are very similar , But it's more flexible . It can specify different files in different search directories . It's a very flexible feature . It can be used in three ways ：

1 . Specify the search directory for files that match the pattern .

vpath <pattern> <directories>

2 . Clear the search directory for files that match the pattern .

vpath <pattern>

3 . Clear all file search directories that have been set up .

vpath

vapth The use method needs to include “%” character .“%” It means to match zero or several characters , for example ,“%.h” All in the form of “.h” Final document . Specifies the file set to search for , And then specify the search directory of the file set . for example ：

vpath %.h ../headers

This statement means , requirement make stay “…/headers” Search the directory for all of the “.h” Final document .（ If a file is not found in the current directory ）

3. vpath Different search strategies

We can use it continuously vpath sentence , To specify different search strategies .
If it's continuous vpath The same occurs in the statement , Or repeated , that ,make According to vpath Execute the search in the order of statements . Such as :

vpath %.c foo
vpath % blish
vpath %.c bar

It said “.c” Final document , First in “foo” Catalog , And then there was “blish”, And finally “bar” Catalog .

vpath %.c foo:bar
vpath % blish

The above statement means “.c” Final document , First in “foo” Catalog , And then there was “bar” Catalog , The last is “blish” Catalog .