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Today, I will talk to you about the example analysis of Linux dynamic library and static library, which may not be well understood by many people. in order to make you understand better, the editor has summarized the following content for you. I hope you can get something according to this article.

Function libraries are divided into static libraries and dynamic libraries. The creation and use of Linux static libraries and Linux dynamic libraries are detailed here in the form of examples. The static library will be connected to the object code when the program is compiled and will no longer be needed when the program runs. The dynamic library is not connected to the object code when the program is compiled, but is loaded when the program is running, so the dynamic library still needs to exist when the program is running.

Step 1: edit the programs that are given examples-hello.h, hello.c and main.c

Hello.h (see Program 1) is the header file of the function library.

Hello.c (see Program 2) is the source of the function library, which contains the common function hello, which will output "Hello XXX!" on the screen.

Main.c (see Program 3) is the main program of the test library file, and the common function hello is called in the main program.

Program 1: hello.h # ifndef HELLO_H # define HELLO_H void hello (const char * name) # endif / / HELLO_H-Program 2: hello.c # include void hello (const char * name) {printf ("Hello% s!\ n", name) }-Program 3: main.c # include "hello.h" int main () {hello ("everyone"); return 0 }

Step 2: compile hello.c into a .o file

Both static and dynamic libraries are created by .o files. Therefore, we must first compile the source program hello.c into a .o file through gcc. Type the following command at the system prompt to get the hello.o file.

# gcc-c hello.c

Step 3: create a static library from a .o file

The naming convention for static library filenames is prefixed with lib, followed by static library names with a .an extension. For example, if the static library we will create is named myhello, then the static library file name is libmyhello.a. You need to be aware of this when creating and using static libraries. Create a static library with the ar command. Typing the following command at the system prompt creates the static library file libmyhello.a.

# ar cr libmyhello.a hello.o

Step 4: use static libraries in your program

Now that the static library is finished, how to use its internal functions? You only need to include the prototype declaration of these common functions in the source program that uses these common functions, and then specify the static library name when you generate the target file with the gcc command, and gcc will connect the common functions to the target file from the static library. Note that gcc prefixes the static library name with lib, and then appends the static library file name obtained by the extension .a to find the static library file. In the program 3:main.c, we include the header file hello.h of the static library, and then call the common function hello directly in the main program main. The following is the target program hello, and then run the hello program to see what the result is.

# gcc-o hello main.c-L. -lmyhello

#. / hello

Hello everyone!

#

Let's delete the static library file and see if the common function hello is actually connected to the target file hello.

# rm libmyhello.a

Rm: remove regular file `libmyhello.a'? Y

#. / hello

Hello everyone!

#

The program runs as usual, and the common functions in the static library are connected to the object file. Let's move on to how to create dynamic libraries in Linux. Let's start with the .o file.

Step 5: create a dynamic library file from a .o file

The dynamic library file name naming convention is similar to the static library file name naming convention, which also adds the prefix lib to the dynamic library name, but its file extension is .so. For example, if the dynamic library we will create is called myhello, then the file name of the dynamic library is libmyhello.so. Use gcc to create dynamic libraries. Type the following command at the system prompt to get the dynamic library file libmyhello.so.

# gcc-shared-fPCI-o libmyhello.so hello.o

Step 6: use dynamic libraries in your program

Using a dynamic library in a program is exactly the same as using a static library, including the prototype declaration of these common functions in the source program that uses these common functions, and then indicating the dynamic library name to compile when you generate the target file with the gcc command. Let's run the gcc command to generate the target file, and then run it to see the results.

# gcc-o hello main.c-L. -lmyhello

#. / hello

. / hello: error while loading shared libraries: libmyhello.so: cannot open shared object file: No such file or directory

#

Ohh! There was a mistake. Look at the error message, it turns out that the dynamic library file libmyhello.so can not be found. When the program is running, it looks for the required dynamic library files in directories such as / usr/lib and / lib. If found, the dynamic library will be loaded, otherwise the program will be terminated with an error similar to the above. Let's copy the file libmyhello.so to the directory / usr/lib and try again.

# mv libmyhello.so / usr/lib

#. / hello

Hello everyone!

#

Succeed. This further illustrates that dynamic libraries are needed when the program is running.

We look back and find that using a static library is exactly the same as using a dynamic library to compile into a target program using the gcc command. Which library file will the gcc command use when the static library and the dynamic library have the same name? With the feeling that we must get to the bottom of the problem, let's have a try. First delete all files except .c and .h and restore them to the state where we have just finished editing the example program.

# rm-f hello hello.o / usr/lib/libmyhello.so

# ls

Hello.c hello.h main.c

#

Create the static library file libmyhello.an and the dynamic library file libmyhello.so.

# gcc-c hello.c

# ar cr libmyhello.a hello.o

# gcc-shared-fPCI-o libmyhello.so hello.o

# ls

Hello.c hello.h hello.o libmyhello.a libmyhello.so main.c

#

Through the above * ls command, you can find that both the static library file libmyhello.an and the dynamic library file libmyhello.so have been generated and are in the current directory. Then we run the gcc command to generate the object file hello using the function library myhello and run the program hello.

# gcc-o hello main.c-L. -lmyhello

#. / hello

. / hello: error while loading shared libraries: libmyhello.so: cannot open shared object file: No such file or directory

#

It is easy to know from the results of the running of the program hello that when the Linux static library and the Linux dynamic library have the same name, the gcc command takes precedence over the dynamic library.

After reading the above, do you have any further understanding of the example analysis of Linux dynamic and static libraries? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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