ANDROID.MK (2) function advanced Tutorial-branching, looping, subroutines

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function Advanced Tutorial-branching, looping, subroutines

According to the standard process of process-oriented programming, we have finished the sequential structure, we need to talk about branching, looping and subroutines. Let's start with the functions used for branching, looping, and subroutine invocation functions.

Branch functions

To go to the branch, must be conditional to judge.
In makefile, the main judgment is to see if the string can be found.
The FindString function is used to make this judgment, and then uses the IF function to use the result of the FindString function.

Cases:

$(findstring boot.oat,$(bootoatfile))result_findString2 := $(findstring boot.oat,$(oatfile))all5 : $(if $(result_findString), @echo found boot.oat, @echo cannot find boot.oat) $(if $(result_findString2), @echo found boot.oat, @echo cannot find boot.oat)

Output:
Found Boot.oat
Cannot find Boot.oat

Loop function

The support for loop structures in makefile is the foreach function
The syntax format is: $ (foreach variable, list, action on variable pair)

Such loops are everywhere in the android.mk, such as traversing a module, traversing a product, and so on.

Let's look at an example, this example is written in build/core/main.mk:

# A helper goal printing out install paths.PHONY: GET-INSTALL-PATHGET-INSTALL-PATH:    @$(foreach m, $(ALL_MODULES), $(if $(ALL_MODULES.$(m).INSTALLED), echo ‘INSTALL-PATH: $(m) $(ALL_MODULES.$(m).INSTALLED)‘;))

Look at a more complicated, deeper impression:

# A static Java library needs to explicily set LOCAL_RESOURCE_DIR.ifdef LOCAL_RESOURCE_DIRneed_compile_res := trueall_resources := $(strip     $(foreach dir, $(LOCAL_RESOURCE_DIR), $(addprefix $(dir)/, $(patsubst res/%,%, $(call find-subdir-assets,$(dir)) ) ) ))

Subroutine calls

The subroutine structure of makefile is of course the function.

Defining a function is as simple as defining a variable. Parameters can be represented by $ (1), $ (2), etc.
Cases:

$(findstring boot.oat,$(1))

When calling, be aware that the call function is called with a space between the calls and function names, after which the arguments are separated by commas.

Let's look at a simple example that encapsulates the function of the findstring mentioned above as a function.
Cases:

$(findstring boot.oat,$(1))all6 :    $(if $(call isBootOat,$(bootoatfile)), @echo found boot.oat, @echo cannot find boot.oat) $(if $(call isBootOat,$(oatfile)), @echo found boot.oat, @echo cannot find boot.oat)

Output:
$ make All6
Found Boot.oat
Cannot find Boot.oat

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ANDROID.MK (2) function advanced Tutorial-branching, looping, subroutines