Creation and use of Linux static libraries and dynamic libraries (shared libraries) (attention to coverage issues)

One, the Linux operating system support function library Branch

Static libraries: LIBXXX.A, compiling libraries into executable programs at compile time

Advantage: No external function library is required in the program's running environment

Cons: Large executable program

Dynamic libraries: Also known as shared libraries, libxxx.so, loading libraries into executable programs while the program is running

Advantages: Small Executable Program

Disadvantage: The corresponding library must be provided in the running environment of the program

function Library Catalog:/lib/usr/lib

Second, the production of Static library

① generating the target file: Gcc-c file.c

② Creating a static library command AR

AR-CR Libfile.a FILE.O

The meaning of-c:crete

-r:replace means that when the inserted module FILE.O already exists in Libfile.a, it is overwritten. Conversely, AR displays an error message.

③ several examples of operating static libraries:

Scenario 1: If you get a static library Libunknown.a from Elsewhere, you want to know which modules are included.

Command---ar-t libunknown.a

Compile the Static library: Gcc-o main main.c-l. -lfile compiled MAIN.C will integrate the static library into main.

which

-L: Specifies the location of the static function library for lookup, and note that there is a later. , which indicates that the static library is looking in the current directory.

-L: The static library name is specified, because the static function library is named Lib***.a, where Lib and. A can be ignored.

④ Example

　　　

　　　

　　　

　　　

Three, the production of dynamic library

① generating the target file: Gcc-c file.c

②gcc-shared-fpic-o libfile.so FILE.O

-fpic: Generating location-independent code

-shared: Generating a shared library

Use the above command to generate the libfile.so dynamic function library.

Gcc-o out Main.c-l. -lfile

It is not yet possible to execute immediately./out, because when used in a dynamic library, the dynamic library is found by default in the/usr/lib or/lib directory, while the libraries we generate are not inside

③ Example

　　　　

　　　　

The first method:

Libfile.so side to/lib or/usr/lib.

The second method: The method of environment variables, assuming libsub.so in ~/coding/libsotest

Execute Export ld_library_path=~/coding/libsotest

Echo $LD _library_path to see if the path was added successfully

　　　　

Third method: Modify the Sheel configuration script

Add our generated library directory to the/etc/ld.so.conf file and/sbin/ldconfig

/etc/ld.so.conf is a very important directory that contains the directories that the linker and the loader will check when searching for shared libraries, by default from/usr/lib

Or/lib, so if you want to run smoothly, you can add the directory of our library to this file and execute the/sbin/ldconfig

① Open ld.so.conf File

　　　　　　

② adding a path to a file

　　　　　　

③ execute Sheel script with Ldconfig

　　　　　　

④ Executing an executable program

　　　　　　　　　　

Iv. comparison of the size of static and dynamic libraries

　　　　　　

Thus:

Compile successfully after executable program, static cubby large, because there is not much code here, so see there is a big gap

Http://www.cnblogs.com/jiangson/p/6077171.html

Creation and use of Linux static libraries and dynamic libraries (shared libraries) (attention to coverage issues)