Detailed explanation of the functions of -I (uppercase i), -L (uppercase l), and -l (lowercase l) when compiling programs with g++ under Linux

As an entry-level Linux user, I have used simple gcc/g++ operations many times, but sometimes libraries are used for slightly more complex programs. When I encountered a problem, I looked up a lot of information summarized by my predecessors, and left a script hoping it would be helpful to my friends. I'd be very happy if I could solve your problem too, hehe.
For example: libz.so

g++ -o compress compress.cpp -I/home/include/ -L/lib/ -lz

(1) -I (uppercase i)

The compiler searches for header files in the path specified by -I.

-I/home/include/ means that -I/home/include/ directory is used as the first directory to search for header files. The search order is:

/home/include/ -->/usr/include -->/usr/local/include

(2) -L (uppercase l)

It means: the compiler searches for the library file in the path specified by -L. Generally, you can use -l to specify multiple library files at once after -L.

-L/lib/ means to search for library files in the /lib/ directory

(3) -l (lowercase l)

It means: the compiler searches the system default path. If it cannot find the library, it searches the current directory. If it cannot find the library in the current directory, it searches the path set to the top of the environment variables such as LD_LIBRARY_PATH . If it still cannot find the library, the compiler prompts that it cannot find the library.

This example uses the gunzip library, the library file name is libz.so, and the library name is z. It is easy to see that removing the first lib and the last .so of the library file name gives you the library name.

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