What is the difference between dynamic libraries and static libraries in linux

Difference: 1. The static library will be connected to the target code when the program is compiled, and the static library will no longer be needed when the program is run; the dynamic library will not be connected to the target code when the program is compiled. , but is loaded when the program is running, so the dynamic library needs to exist when the program is running. 2. The files generated by dynamic libraries are relatively small, and the files generated by static libraries are relatively large.

The operating environment of this tutorial: CentOS 6 system, Dell G3 computer.

The similarities and differences between dynamic libraries and static libraries in Linux

The similarities:

Both static libraries and dynamic libraries are created by .o files. Therefore, we must first compile the source program into an .o file through gcc;

Difference:

1. Code loading The time is different

• The static library will be connected to the target code when the program is compiled,The static library will no longer be needed when the program is running;
• The dynamic library will not be connected to the target code when the program is compiled, but will be loaded when the program is running, so the dynamic library needs to exist when the program is running

2. Different compilation rules

• Dynamic library compilation

The name of the dynamic class library is generally libxxx.so, and the dynamic function library is in It is not compiled into the target code during compilation. Your program only calls the corresponding function in the function library when it reaches the relevant function. Therefore, the executable file generated by the dynamic function library is relatively small;

Dynamic When compiling the library: The most important thing is an option on the GCC command line. -shared This option specifies the generation of a dynamic link library, for example:

g -shared -o libd1.so d1.o /*Create dynamic library file d1.so based on intermediate target file d1.o*/

g -shared -o libd2.so d2.o /*Create dynamic library file d2 based on intermediate target file d2.o. so*/

• Static library compilation

The name of the class library is generally libxxx.a; the file compiled using the static function library is relatively large, because the entire function library All data will be integrated into the target code, and its advantage is obvious, that is, the compiled execution program does not require external function library support, because all functions used have been compiled in. Of course, this will also be its disadvantage, because if the static function library changes, your program must be recompiled.

In UNIX, use the ar command to create or operate a static library

ar archivefile objfile

archivefile: archivefile is the name of the static library

objfile :objfile is an intermediate target file name with an extension of .o, which can be multiple in parallel;

For example:

g++ -o hello.o -c hello.cpp
ar cqs libHello.a hello.o

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