The C language function library is a toolbox containing various functions, which are organized in different library files. Adding a library requires specifying it through the compiler's command line options, for example, the GCC compiler uses the -l option followed by the abbreviation of the library name. If the library file is not under the default search path, you need to use the -L option to specify the library file path. Library can be divided into static libraries and dynamic libraries. Static libraries are directly linked to the program at compile time, while dynamic libraries are loaded at runtime.

C language function library? This question is awesome! Many beginners are confused and think that this thing is like a ghost, invisible and intangible. In fact, it is right next to you, but you just haven't discovered its true face.

First of all, we have to understand that the C language function library is not a separate file, it is more like a huge toolbox, filled with various functions, which are organized in different library files. These library files, usually .a or .so suffix files (static and dynamic libraries), are hidden in your system, and their location depends on your operating system and compiler.

For example, in Linux systems, commonly used library files are usually located in directories such as /usr/lib , /lib or /usr/local/lib . Under Windows, they may be in directories like C:\Program Files\...\lib . You have to know that this is not static. The location of library files may vary greatly for different systems and compilers.

So, instead of trying to find these library files, it is better to tell the compiler where to find it. This is the key to adding a C function library. This is usually achieved through the compiler's command line options.

Take the GCC compiler for example, you can use the -l option to specify the library you need to link to. For example, if you want to use the math function library math.h , you need to add the -lm option in the compile command. Note that m in -lm is the abbreviation of the library name math , not the file name. This is a conventional rule, you have to remember it.

The complete compile command might look like this:

 <code class="bash">gcc myprogram.c -lm -o myprogram</code>

Here, myprogram.c is your source code file, -lm tells the compiler to link the math library, -o myprogram specifies the output executable file name.

If you need to link multiple libraries, just list the library names in turn after the -l option, for example:

 <code class="bash">gcc myprogram.c -lm -lc -o myprogram</code>

This links the math library and the C standard library ( libc ).

But there is a pit here, and many novices are prone to falling into it: the library file path is incorrect. If your library file is not in the compiler's default search path, you have to tell the compiler the specific location of the library file. This can be achieved with the -L option.

For example, if your library file is located in the /home/user/mylibs directory, then the compilation command should look like this:

 <code class="bash">gcc myprogram.c -L/home/user/mylibs -lmylib -o myprogram</code>

Here, -L/home/user/mylibs specifies the search path of the library file, and -lmylib specifies the library name.

Remember, library names are usually names that remove lib prefix and .a or .so suffix. This is easy to confuse, so be careful.

Finally, let me mention a little more about the difference between static libraries and dynamic libraries. The static library will be directly linked to your program at compile time to generate an independent executable file; while the dynamic library will be loaded at runtime, and your program will depend on the dynamic library files that exist in the system. The advantage of dynamic libraries is that they save space, and multiple programs can share the same dynamic library; but the disadvantage is that if the system lacks the necessary dynamic libraries, your program will not run. Which type of library to choose depends on your specific needs. This requires you to have a deeper understanding of the system. In short, the use of C function library is full of details and skills, which requires you to learn and practice continuously to master. Don’t be afraid to make mistakes. Learning from mistakes is the fastest way to make progress.

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