[basic] the difference between dynamic link library and static link library

One 、 Introduction to static link library and dynamic link library

1. C or C++ The program needs to go through... From source file to executable file 4 Stages
   They are pretreatment 、 compile 、 Compilations and links .
   The work to be completed in the link stage , It is to integrate the object file generated by each source file in the same project and the library file used in the program into an executable file .

2. Although library files are explicitly used for link , But the compiler provides 2 A way to link , They are called static links and dynamic links respectively .
   Use the static link method to realize the link operation , The library file of is called static link library ;
   Use dynamic link to realize link operation , The library file of is called dynamic link library .

3. stay Linux In the distribution system , The suffix of the static link library file is general Commonly used .a Express , The suffix of dynamic link library is general Commonly used .so Express ;
   stay Windows In the system , The suffix of the static link library file by .lib, The suffix of dynamic link library by .dll.

4. GCC When the compiler generates an executable , By default, the dynamic link library will be used first to realize the link operation , Unless there is no dynamic link library required by program files in the current system environment ,GCC The compiler will select the corresponding static link library . If there are neither （ perhaps GCC Compiler not found ）, Then the link fails .

5. stay Linux Distribution in , Static link libraries and dynamic link libraries are usually stored in /usr/bin perhaps /bin Under the table of contents
   

Two 、 difference

1、 Static link library

• The way of static link library to realize link operation is very simple , That is, where is used in the program file Function modules in library files ,GCC The compiler will translate the template code , Directly copy to the appropriate location of the program file , Final generation of executable .
• Static library in Link phase , Will Assemble the generated object file .o Link and package to executable file together with the referenced Library .

advantage ：
Strong portability , Can operate independently , That is, the generated executable file can run independently without the support of any static library file .
Executable programs are no longer related to library functions , It can be implemented in any environment .

Inferiority ：
Code redundancy 、 The size of the executable file is large ： If the same function module in the library is called multiple times in the program file , Then the module code will be copied many times , The generated executable file will contain multiple identical pieces of code , Make code redundant . Compared with the executable generated by dynamic link library , The executable file generated by the static link library is larger .
And if the static library used is updated and changed , Your program must be recompiled .

2、 Dynamic link library

• Dynamic link library , Also known as shared link library . When using dynamic link library to realize link operation , Where does the function module of the library file need in the program file ,GCC compiler The code of this function module will not be directly copied to the file , Instead, the location information of the functional module is recorded in the file , Directly generate executable file .

• obviously , The executable generated in this way cannot run independently . The executable file generated by dynamic link library runs ,GCC The compiler will load the corresponding dynamic link library into memory , Because the location information of the required functional modules is recorded in the executable file in advance , So with the support of the existing dynamic link library , It can also run successfully .

• If the static library liba.lib Updated , So applications that use it all need to be recompiled , It could be a small change , It causes the whole program to download again , Full update .

• Dynamic libraries are not connected to the target code when the program is compiled , It's loaded when the program is running .
  Different applications call the same library , Only one instance of the shared library is needed in memory , Avoid the problem of space waste . Dynamic library is loaded when the program is running , It also solves the update of static library to program 、 Trouble deploying and publishing pages . Users only need to update the dynamic library , Incremental updating .

advantage ：
Generated The execution file is small , Because the executable file records the address of the function module , The real implementation code will be loaded into memory when the program is running , Even if the function module is called many times , Using the same implementation code （ This is why dynamic link libraries are called shared link libraries ）.
Dynamic library changes do not affect your program , Therefore, it is more convenient to upgrade the dynamic function library .
Inferiority ：
Poor portability , Can't run independently , You must use the corresponding library files .

https://blog.csdn.net/oqqHuTu12345678/article/details/125083174

https://www.bilibili.com/read/cv15423597/

https://blog.csdn.net/breakpoints_/article/details/116166379