Two mysterious tools in Linux: static libraries vs dynamic libraries

In the Linux world, programmers often use two mysterious tools - static libraries and dynamic libraries. What are the advantages and differences between the two? How to choose wisely according to project needs?

1. The concept of static library and dynamic library

First, let us briefly understand the basic concepts of these two.

• Static library: A static library links the library code and program code together during compilation to form an independent executable file. All code is packaged into the final executable file, allowing the program to run without relying on external libraries.
• Dynamic library: A dynamic library is a library that is loaded when the program is running. It does not contain the library code when the program starts, but is loaded when needed. Multiple programs can share instances of the same dynamic library, saving memory space.

2. Static library vs dynamic library: Comparison of advantages

Advantages of static libraries:

• Strong independence: The static library packages all codes into executable files. The program does not require external support when running and has strong independence.
• Fast linking speed: Since all codes are linked when compiled, the linking speed of static libraries is relatively fast.
• Good portability: Because all dependencies are packaged, the program is easier to port on different systems.

Advantages of dynamic libraries:

• Strong sharing: Multiple programs can share instances of the same dynamic library, saving memory and improving system performance.
• High flexibility: can be loaded and unloaded while the program is running, no need to recompile the program, easier to update and maintain.
• Runtime loading: Dynamic library loading is performed while the program is running, providing greater flexibility.

3. Difference comparison: static library vs dynamic library

Compilation method:

• Static library: Linked with program code at compile time to generate an independent executable file.
• Dynamic library: Loaded by the dynamic linker at runtime, the program does not contain the library code when it is started.

File extension:

• Static library: usually with .a extension, such as libexample.a.
• Dynamic library: usually with .so extension, such as libexample.so.

Memory usage:

• Static library: The entire library code is embedded in the executable file and may occupy more memory.
• Dynamic library: Multiple programs can share an instance of a library to save memory.

Updates and Maintenance:

• Static library: The program needs to be recompiled to update the library, which is not flexible enough.
• Dynamic library: The library can be updated without recompiling the program, making maintenance more convenient.

4. Comparison of usage scenarios: static library vs dynamic library

Applicable scenarios for static libraries:

• High independence requirements: When the program has high requirements for independence and does not rely on external libraries, choosing a static library is a good choice.
• Strict version requirements: When a program requires a specific version of a library, embedding the library code into the program can ensure version consistency.

Applicable scenarios for dynamic libraries:

• High sharing requirements: When multiple programs need to share instances of the same library, using dynamic libraries can reduce system memory usage.
• High flexibility requirements: When the program needs to update the library without recompiling, it is more appropriate to choose a dynamic library.

5. Case Analysis

Scenario: Suppose we have a graphics processing program that needs to load the function of different filters.

1. How to use static libraries

Each filter can be compiled into a static library and then linked into the main program.

gcc -c filter1.c -o filter1.o
ar rcs libfilter1.a filter1.o
gcc -o image_editor main.c -L. -lfilter1

In this way, the code of each filter is packaged into the main program to form an independent executable file.

2. How to use dynamic libraries

If we choose to use a dynamic library, each filter can be compiled into a dynamic library and loaded when the program is running.

gcc -shared -fPIC filter2.c -o libfilter2.so
gcc -o image_editor main.c -ldl

When the program is running, dynamic libraries of different filters can be loaded through the dynamic linker to achieve more flexible filter management.

6. Conclusion

On the road of exploring Linux, static libraries and dynamic libraries are your right-hand assistants. Understanding their pros and cons and choosing wisely will help your program become more powerful and flexible.

The above is the detailed content of Two mysterious tools in Linux: static libraries vs dynamic libraries. For more information, please follow other related articles on the PHP Chinese website!