Basic IO (below): soft and hard links and dynamic and static libraries

"There is no easy,Only the unreached shore" 

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 (1)理解文件系统

①inode:

in the process chapter,我们知道.The system will create multiple processes,need to manage.

The six-character mantra of management: 先描述 再组织 

每个进程都有对应的pid,Make it easier for the operating system to manage itself.

So relative to the file,you can find in different directories,can create a file with the same name.本质上,These files are not only identified by the file name.but hidden inode.

inode 就 类似于 进程的 pid 

ls -l -i //带上-i 选项 查看 文件的inode

 那么inode where do the numbers come from?？

 

②Disk partition:

磁盘是典型的块设备,and almost the only mechanical equipment.

disk storage partition:

分区	作用
超级块（Super Block）	记录的信息主要有：bolck 和 inode的总量, 未使用的block和inode的数量,一个block和inode的大小,最
块组描述符(GDT)	描述块组属性信息
块位图(Block Bitmap)	记录Data blockWhich piece of data is occupied Which piece of data is not occupied
inode位图(inode Bitmap)	每个bit表示一个inode是否空闲可用
inode table	original file information
Data block	数据区

 

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(2)软硬链接:

①How to understand hard links?

我们知道,The real file on the disk is not the filename,而是inode. 然而在linux下,Multiple file names can correspond to the sameinode.

ln +目标文件 +当前文件 // 硬链接
ln + (-s)             //软连接

The fundamental difference between hard and soft link:

Hard links do not generate new onesinode,Also, it is not a separate file.

Soft link will be newly created 新的 inode  ,是一个独立的文件.

We delete separately hard and soft link 原文件:

The original file is “干掉”:

软链接的 The file can no longer be used.

硬链接 Can continue to use the file. 

 

②inode中的ref

struct inode
{
  int ret; //引用计数
}

 

在dycreate another directoryclass 目录后: 

 

 也就是说,hardwired properties 是在包括“."    "..”,When creating another inside the directory class.

 

③ACM文件时间;

stat  + 文件名

Access;最后访问时间

Modify;文件最后修改时间

Change;属性修改时间 

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(3)动静态库: 

①动静态库

linux下

静态库; .a

动态库; .so

win下;

动态库:.dll

静态库: .lib

 

②Dynamic and static library features:

 

静态:

①static library linking because 在编译时,All code needs to be loaded into memory.占用空间很大(内存+磁盘)

②When calling the same static library,会出现重复代码.代码冗余.

动态:

依赖动态库.No library will not be able to use library content.

③如何制作动静态库？

静态库:

We make dynamic and static libraries,只需要把头文件、.oJust pack the file.

   //Makefile 
   //mylib 是 libcal.a的别名
   //CC 是gcc的别名
   mylib=libcal.a
   CC=gcc
   
   //编译mylib 也就是 libcal.a
   $(mylib):add.o sub.o
     ar -rc $(mylib) $^    //here is a must！！！
  
  //%. 通配符
   %.o:%.c  
     $(CC) -c  $<
                
.PHONY:clean
clean:
   rm -rf $(mylib) *.o
   rm -rf mathlib


//创建目录 并把编译好的.o .h copy directory
.PHONY:output
output:
   mkdir -p mathlib/lib
   mkdir -p mathlib/include
   cp *.h mathlib/include
   cp *.a mathlib/lib

 我们需要的就是 把mathlib Just throw it away.

 此时我们对 文件进行编译.发现无法找到<add.h>的头文件.

这很好理解.

The compiler can only search in the default path.

//编译

gcc +(mytest.c) -I 头文件  -L 库路径 -l specific library

We generate a static library.

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动态库:

Same as static library;

但编译.c \.so文件;

//.c  -> .o
gcc -fPIC

//.o -> libcal.so
gcc -shared

.o生成 

 libcal.so

 

We successfully compiled the file But why don't run up？！ 

 

根本上,编译和执行是分离的,One is to hand over to the compiler,The other is to hand over to the operating system

We tell the compiler only 这个mytest.cwhere are the library files for. 但是 When the file is run and becomes,The operating system cannot find the library file！！

 

导入环境变量:

echo$ LD_LIBRARY_PATH：System library default path



export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:+库的绝对路径

 导入前:

 

导入后,执行了. 

 

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总结:

①inode作为文件标识符.Can be pointed to by multiple files at the same time.

②软链接会创建新的inode 反而 Hard links do not

③静态库制作:

ar -rc 

-I -L -l

④动态库制作:

-fPIC

-shared

-l

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This is the end of this article~

感谢你的阅读.

祝你好运~