Common configuration techniques for implementing dynamic link libraries under Linux

Common configuration techniques for implementing dynamic link libraries under Linux

Dynamic Link Library (DLL for short) is a code and resource library that can be shared between multiple programs. In the Linux system, the dynamic link library is called a shared library (Shared Library). By separating the code and resources from the program, the reusability of the code and the running efficiency of the program can be improved. This article will introduce common configuration techniques for implementing dynamic link libraries under Linux and give corresponding code examples.

1. Create a dynamic link library

In the Linux system, creating a dynamic link library requires the following steps:

1. Writing source code: Create a file that needs to be shared Code and resource files, such as functions, variables, constants, etc.
2. Write a compilation script: Create a script file for compiling and linking the dynamic link library, usually a Makefile.
3. Compile link: execute the compilation script to compile the source code into a dynamic link library.

The following is a simple example showing how to create a simple dynamic link library:

First is the source code of the dynamic link library, we create a file called libhello.c file, which contains a function named hello:

#include <stdio.h>

void hello()
{
    printf("Hello, World!
");
}

Next is the compilation script Makefile, the content is as follows:

CC = gcc
CFLAGS = -Wall -shared -fPIC

libhello.so: libhello.c
    $(CC) $(CFLAGS) $^ -o $@

Execute the make command on the command line, The dynamic link library libhello.so can be generated.

2. Using the dynamic link library

Using the dynamic link library also requires several steps:

1. The header file contains: In the code that needs to use the dynamic link library , including the header files of the dynamic link library.
2. Configure link options: When compiling and linking code, add link options for dynamic link libraries.
3. Call function: Use the function in the dynamic link library by calling its function in the code.

The following is a simple example showing how to use the dynamic link library just created:

First, using the source code of the dynamic link library, we create a file named main. c file, which contains code that calls the hello function in the dynamic link library.

#include <stdio.h>
#include "libhello.h"

int main()
{
    hello();
    return 0;
}

The next step is the compilation script Makefile, the content is as follows:

CC = gcc
CFLAGS = -Wall -L. -lhello

main: main.c
    $(CC) $(CFLAGS) $^ -o $@

Execute the make command on the command line to generate the executable file main. Run this program and you will see "Hello, World!" printed out.

3. Common configuration techniques for dynamic link libraries

1. Naming of dynamic link libraries

When creating a dynamic link library, lib is usually used as the prefix ,.so as extension. For example, in the above example, we use libhello.so as the name of the dynamic link library. This is a naming convention that helps distinguish dynamic link libraries from other types of files.

2. Version control of dynamic link libraries

In order to facilitate version control of dynamic link libraries, you can add the version number to the name of the dynamic link library. For example, libhello.so can be changed to libhello.so.1, which represents the dynamic link library with version number 1. At the same time, you can also use -fvisibility=hidden during compilation to hide symbols in the dynamic link library that do not need to be exposed to the outside world.

3. Dynamic link library path configuration

When using a dynamic link library, the operating system needs to know the path of the dynamic link library. You can configure the path of the dynamic link library in the following ways:

• Copy the dynamic link library to a standard library path, such as /usr/lib or /usr/local/lib.
• Use the -L option to specify the path to the library when compiling, such as -L/opt/libs.
• When the program is running, specify the search path for the dynamic link library by setting the LD_LIBRARY_PATH environment variable, such as export LD_LIBRARY_PATH=/opt/libs.

Through the above configuration techniques, common configurations of dynamic link libraries can be implemented in Linux systems.

4. Summary

Through the introduction of this article, we have learned how to implement common configuration techniques of dynamic link libraries under Linux. Dynamic link libraries can improve code reusability and program operating efficiency, and are a common technology in software development. I hope this article will help you use dynamic link libraries under Linux and provides corresponding code examples.

Reference materials:

1. http://www.runoob.com/linux/linux-libraries.html
2. https://zh.wikipedia.org /wiki/Dynamic Link Library

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