Makefile variables and dynamic library static library

One 、Makefile Variable

1. Makefile Predefined variables of

Variable name	meaning
AR	Function library packer , You can create a static library .a file . The default is ar
AS	assembler , The default is as
CC	C compiler , Default gcc
CXX	C++ compiler , Default g++
CPP	C The preprocessor of the program , The default is $(CC) -E
RM	The delete command , The default is rm -f
ARFLAGS	perform AR Command line arguments for the command , Default rv
ASFLAGS	Assembler AS Command line parameters of ( Specify clearly .s or .S When you file )
CFLAGS	perform CC Compiler command line arguments ( compile .c Source file options )
CXXFLAGS	perform g++ Compiler command line arguments ( compile .cpp Source file options )

2. Makefile Automation variables of

Variable name	meaning	remarks
@ （ file name ）	The full name of the target representing the rule in which it is located
% （ file name ）	A member name of the static library file that represents the rule it is in
< （ file name ）	Represents the first full name of the dependency list of the rule in which it is located
* （ file name ）	In pattern rules and static pattern rules , Stands for stem	Stem time target mode ”%” Say the representative part . When the file name exists in the directory , Stems can also contain directories
? ( File list )	List of dependent files whose timestamp is newer than the target file , Separate with spaces
^ ( File list )	Represents the dependency list of the rule in which it is located	The same file cannot be repeated
+ ( File list )	Represents the dependency list of the rule in which it is located	The same file can be repeated , Mainly used in program linking , The cross reference place of the Library

3. Makefile A variant of the automation variable

Variable name	meaning	remarks
@D	Represents the directory part of the target file ( Remove the last slash in the directory section )	If $ @ yes dir/foo.o, that $(@D) The value of is dir; If [email protected] There are slashes , Its value is the current directory (.); Notice how it relates to functions dir The difference between
@F	The part of the full file name of the target file other than the directory （ Actual filename ）	If $ @ yes dir/foo.o, that $ (@F) Namely foo.o; $ (@F) It's equivalent to a function $(notdir [email protected])
*D	Represents the directory part in the target stem
*F	Represents the file name part in the target stem
%D	When archive(member) When the formal static library is the target , Table library file members member The directory part of the name	Only on archive(member) Formal rule objectives are valid
%F	When archive(member) When the formal static library is the target , Table library file members member The file name part of the name	Only on archive(member) Formal rule objectives are valid
<D	Represents the directory part of the first dependent file in the rule
<F	Represents the file name part of the first dependent file in the rule
^D	Represents the directory part of all dependent files	The same file cannot be repeated
^F	Represents the file name part of all dependent files	The same file cannot be repeated
+D	Represents the directory part of all dependent files	The same file can be repeated
+F	Represents the file name part of all dependent files	The same file can be repeated
?D	Represents the directory part of the updated dependent file
?F	Represents the file name part of the updated dependent file

4. Makefile Operation and use of

#  Execute specified Makefile Almake yes makefile The name of 
$ make -f ALmake
$ make --file Almake 
$ make --makefile Almake
$ make TARGET      # Specify the ultimate goal 
# Force the reconstruction of targets in all rules 
$ make -B
$ make -always-make
# Appoint makefile The path of 
$ make -C dir/
$ make --directory=dir/

# GNU-autotools Tools （ automation makefile）
# GNU Trilogy of software installation 
$ ./configure
$ make
$ make install

Two 、 Dynamic and static libraries

1. Understanding of static library and dynamic library

• Static library :Linux With .a A file with a suffix name (win Of lib file )
  Static library in gcc The link phase of is integrated into an executable program . Even if the library is deleted , The program can still run successfully . But it's big .
  Copy the static library loader when the program is loaded , So the volume is large .
• Dynamic library ：Linux With .so A file with a suffix (win Of dll file )
  The dynamic library does not belong to any program , Any program can share this library , When the program is running , Only link library . Small volume .
• Linux Rules for dynamic libraries in the naming system of
  libname.so.x.y.z
  lib: Fixed representation Library name: Library name so: Fixed suffix x: The major version number y: Sub version number z: Release number
  The main version is incompatible during version upgrade （ The main version number is different ）
  Next version update software , Keep the original program , Add functionality （ Version numbers are downward compatible ）
  Release performance changes , Program optimization ;（ Mutual compatibility ）

2. The creation and use of static library （ar command ）

# ar Common parameters of 
$ ar  -ctr   libtest.a   *.o  # Put all... In the current directory .o Files are packaged into static libraries libtest.a
#ar  Parameters of  
# -r  Insert the file into the library file , If it already exists, replace ;
# -t  View all packaged .o file 
# -c  Representation creation ,create
$ gcc  main.c  libtest.a  -o main   # Use static libraries 

3. The creation and use of dynamic library

$ gcc  -fPIC  -shared   *.c  -o   libtest.so  # Create a dynamic library 
# -fPIC  Means to generate independent code  PIC Tell the compiler to generate location independent code , That is, the memory is not fixed .
# -shared  Means to generate a shared dynamic library  
$ gcc  main.c  ./libtest.so  -o main  -I  ./inc  # Link dynamic library to generate execution file main, but main The dynamic library must exist when executing .
# Dynamic library defaults to real system lib In looking for , The generated dynamic library can be used in the system lib in ; You can also add $LD_LIBRARY_PATH  Environment variables of can also be added to this directory .
#  Add environment variables export LD_LIBRARY_PATH=/home/gec/Linux/ku:$LD_LIBRARY_PATH 
# /home/gec/lib: Library file path ( The path can be specified according to your own needs ); 
#  Be careful : When encapsulating the dynamic library, the function corresponds to the header file ; Dynamic library should exist ; Dynamic library environment