[skill][makefile] makefile 常用内容记录

其实，makefile有点复杂。

文档看了又看，还是要经常翻，做个记录备忘 ：）

1.  隐含命令 implicit rules

　　与 implicit rule 相对应的有 pattern rules 和 suffix rules

Compiling C programs
n.o is made automatically from n.c with a recipe of the form ‘$(CC) $(CPPFLAGS) $(CFLAGS) -c’.

Compiling C++ programs
n.o is made automatically from n.cc, n.cpp, or n.C with a recipe of the form ‘$(CXX) $(CPPFLAGS) $(CXXFLAGS) -c’. We encourage you to use the suffix ‘.cc’ for C++ source files instead of ‘.C’.

Linking a single object file
n is made automatically from n.o by running the linker (usually called ld) via the C compiler. The precise recipe used is ‘$(CC) $(LDFLAGS) n.o $(LOADLIBES) $(LDLIBS)’.

This rule does the right thing for a simple program with only one source file. It will also do the right thing if there are multiple object files (presumably coming from various other source files), one of which has a name matching that of the executable file. Thus,

x: y.o z.o
when x.c, y.c and z.c all exist will execute:

cc -c x.c -o x.o
cc -c y.c -o y.o
cc -c z.c -o z.o
cc x.o y.o z.o -o x
rm -f x.o
rm -f y.o
rm -f z.o
In more complicated cases, such as when there is no object file whose name derives from the executable file name, you must write an explicit recipe for linking.

CFLAGS
Extra flags to give to the C compiler.

CXXFLAGS
Extra flags to give to the C++ compiler.

CPPFLAGS
Extra flags to give to the C preprocessor and programs that use it (the C and Fortran compilers).

LDFLAGS
Extra flags to give to compilers when they are supposed to invoke the linker, ‘ld’, such as -L. Libraries (-lfoo) should be added to the LDLIBS variable instead.

LDLIBS
Library flags or names given to compilers when they are supposed to invoke the linker, ‘ld’. LOADLIBES is a deprecated (but still supported) alternative to LDLIBS. Non-library linker flags, such as -L, should go in the LDFLAGS variable.

　　Canceling Implicit Rules

定义一个空的 recipe 就可以取消隐含命令：

%.o : %.s

生成 *.o 的隐式命令，就被取消了。