Preliminary introduction to linux programming: the comfort and slimming of Makefile-general Linux technology-Linux programming and kernel information. The following is a detailed description. Make is a magic thing. There are many advanced usage in it. If it is not used, it will be very troublesome to write Makefile. Next we will take a practical example to look at the re-definition of make's (1) implicit pattern rule (2) Automatic dependency generation (3) nested call of make.
1. Assume that a project is divided into two subprojects: gtrans and isgen.
~> Ls project
Gtrans isgen Makefile gtrans isgen // both gtrans and isgen are generated programs.
Project> ls GTRANS/
Makefile findGraph. d findGraph. o gtrans. d isgen. cpp preProcess. d preProcess. o
FindGraph. cpp findGraph. hpp gtrans. cpp gtrans. o preProcess. cpp preProcess. hpp
. D files store the dependency between. o files, and. hpp files store header files.
2. Check GRRANS/Makefile first.
SOURCES = gtrans. cpp findGraph. cpp preProcess. cpp
LIB = "/home/dab/cadlib"
INCLUDE = "/home/dab/cadinc"
VPATH = ..
%. O: %. cpp
$ (CXX)-g3-c $ <-Wall-I $ (INCLUDE)-o $ @
%. D: %. cpp
$ (CXX)-MM-w $ <>@ @; sed's/\ ($ *\)\. o [:] */\ 1.o $ @:/G'-I $ @
Gtrans: $ (SOURCES:. cpp =. o)
$ (CXX) *. o-o ../gtrans-Wl,-R, $ (LIB)-L $ (LIB)-lagraph-lcdt
Include $ (SOURCES:. cpp =. d)
. PHONY: clean
Clean:
Rm ../gtrans *. o
If you do not use the above three functions, Makefile will be very fat. For example, if implicit pattern rule is not redefined, we need to add a compilation command for every *. o: *. cpp rule. The more source files, the more troublesome it will be. If you redefine an Implicit pattern rule (Implicit pattern rule), you will be able to work at a time and enjoy infinite use.
%. O: %. cpp
$ (CXX)-g3-c $ <-Wall-I $ (INCLUDE)-o $ @
This is simple. the default value of the variable CXX is g ++, $ <and $ @ are both automation variables, and $ @ is the file name of the target of the rule; $ <is the name of the first dependency.
3. In Makefile, our dependency may need to contain a series of header files. If it is a relatively large project, you must know which C files contain header files, and when you add or delete header files, you also need to carefully modify the Makefile, this is a very difficult task to maintain. To avoid this heavy and error-prone issue, we can use a C/C ++ compilation function. Most C/C ++ compilers support a "-M" option, that is, to automatically find the header file contained in the source file and generate a dependency. For example
GTRANS> cc-MM gtrans. cpp
Gtrans. cpp: 4: 20: warning: agraph. h: No such file or directory
Gtrans. o: gtrans. cpp findGraph. hpp preProcess. hpp
GTRANS> g ++-MM gtrans. cpp
Gtrans. cpp: 4: 20: warning: agraph. h: No such file or directory
Gtrans. o: gtrans. cpp findGraph. hpp preProcess. hpp
Because gtrans. cpp uses a library file agraph, a warning is prompted. In addition, if a non-standard library is used, two MM options are required. We can use an extreme option-w (the other is-Wall) to disable all warnings.
GTRANS> g ++-MM-w gtrans. cpp
Gtrans. o: gtrans. cpp findGraph. hpp preProcess. hpp
The redefinition of this implicit Pattern Rule is a little complicated because it uses sed, And it will inevitably use Unix regular expressions when sed is used.
%. D: %. cpp
$ (CXX)-MM-w $ <>@ @; sed's/\ ($ *\)\. o [:] */\ 1.o $ @:/G'-I $ @
$ (CXX)-MM-w $ <>$ @; redirects the result. in the d file, use gtrans. d As an example. After redirection, It is gtrans. o: gtrans. cpp findGraph. hpp preProcess. hpp; sed 'script'-I [inputfile] The input file is. d file. The modified results are saved to the file. In the sed script,'s/\ ($ *\)\. o [:] */\ 1.o $ @:/g's/pattern_1/pattern_2/G' indicates replacing all pattern_1 with pattern_2. So \ ($ * \) \. o [:] * and \ 1.o $ @: What are the two patterns respectively?
\ (\) The matching between the two can be saved and used, and a total of nine can be stored. For example, in the above example, one \ 1 is used in the second pattern to use the first \(\) store matched items, that is, the above $ *. $ * Is an automation variable in make. $ * is the stem with which an implicit rule matches, and stem is like %. d. Then this % is stem, matching gtrans. d. Then gtrans are its stem. The character \. Is the character "." (because. is a special character that can match any character). [:] * is an arbitrary number of spaces and.
4. The nested use of make is very simple. Let's take a look at the Makefile example to understand it.
. PHONY: all gtrans isgen cleanall cleanGtrans cleanIsgen
All:
Cd GTRANS & make & cd...; cd ISGEN & make & cd ..
Gtrans:
Cd GTRANS & make
Isgen:
Cd ISGEN & make
Cleanall:
Cd GTRANS & make clean & cd...; cd ISGEN & make clean & cd ..
CleanGtrans:
Cd GTRANS & make clean
CleanIsgen:
Cd ISGEN & make clean
