关于图书馆的一些疑惑

Question

Say, I want to write a program in C++ in Linux and I need some specific libraries. There are 2 ways of getting these libraries:

1. Using the command line--> apt-get install library
2. Downloading and extracting a .zip or .tar file from their website.

Now my questions are:

For the first method I have seen libraries being downloaded with apt-get install library and apt-get install library-dev. I know dev means development or developer, but what is the difference between installing the dev and not installing the dev? What does dev do, exactly?

For the second method, do I need to build the libraries using a compiler? Because I have seen tutorials doing it but the OS used was usually Windows, do I only have to build them on Windows and not Linux?

Also, say I can only use the 2nd method for a certain library and not the first one. After extracting, what am I supposed to do? Is there any default way of installing a library manually or is each library different?

Finally, when I use the first method where is the library installed to? Is it /usr/local/lib, /usr/lib or /usr/include? Because when I have to link to these libraries in the Linker's settings I only write their name, not the path so I assume there is already a default path for libraries to be in.

One last question: Is there any default way of installing and using libraries in general or does that depend on what I want to do, programming language, etc...?

Answer 1

The second method is very broad because it depends entirely on the how the project is designed including the build system used etc. Things get a little more conformant when you use a distribution's managed packages.

If you want to develop a program that uses the library you need the library-dev package that usually contains the C/C++/etc.. header files.

Many development package conform to a standard tool that helps your build system find the libraries header and binary files.

For example libcurl uses the pkg-config system so its compiler components can be found from the command line like this:

pkg-config libcurl --libs # print the library link flags

You can then add that to your Makefile (or whatever build system you use):

program:
     g++ -o program program.cpp $(shell pkg-config libcurl --libs)

The $(shell pkg-config libcurl --libs) part adds the correct compiler flags to link with the library.

Not all dev packaged use pkg-config . Some come with their own tools (like mysql_config ) while others let you guess and try to figure it all out for yourself (looking at you libclang ).