Libraries and their use

This is a discussion on Libraries and their use within the C++ Programming forums, part of the General Programming Boards category; I am a complete newbie but have managed to start learning C++ and am managing quite well using 'Exploring C++ ...

  1. #1
    Registered User
    Join Date
    Jan 2011
    Posts
    101

    Libraries and their use

    I am a complete newbie but have managed to start learning C++ and am managing quite well using 'Exploring C++ by Ray Lischner.
    Using Code::Blocks I type in my listing and run it and have had success; I have even managed to write small programs of my very own.
    However I cannot get my head round libraries and in particular where they are stored and how you know what is in each and suchlike.
    Can anyone reccomend a book which will explain libraries, and especially the differences between say iostream and iostream.h
    Sorry if this is really basic (sic) but then so is my level of understanding.

  2. #2
    Registered User
    Join Date
    May 2011
    Location
    Around 8.3 light-minutes from the Sun
    Posts
    1,866
    No, problem let's just get some terminology down. First, Code::Blocks is an IDE, not a compiler. Take a read through What is a compiler? It should answer most of those questions for you. As for documentation, your compilers documentation is a great place to start to see what is available. Also there are many online resources such as the reference page of C++.com that are readily available.
    Quote Originally Posted by anduril462 View Post
    Now, please, for the love of all things good and holy, think about what you're doing! Don't just run around willy-nilly, coding like a drunk two-year-old....
    Quote Originally Posted by quzah View Post
    ..... Just don't be surprised when I say you aren't using standard C anymore, and as such,are off in your own little universe that I will completely disregard.
    Warning: Some or all of my posted code may be non-standard and as such should not be used and in no case looked at.

  3. #3
    spurious conceit MK27's Avatar
    Join Date
    Jul 2008
    Location
    segmentation fault
    Posts
    8,300
    Quote Originally Posted by JayCee++ View Post
    However I cannot get my head round libraries and in particular where they are stored
    Libraries are compiled executable files. Where they are stored depends on your OS. They may be static or dynamic, aka. shared.

    When you compile your own programs, any static libraries it needs are compiled right into it by the linker. Ie, the linker finds the library and copies it in. On most modern OS's, this is considered inefficient and wasteful, so instead of linking in static libraries, your exe is linked to a shared library. Then, at runtime, the dynamic linker manages the relationship between your program and the shared libraries it is linked to.

    The source for C/C++ libraries are normal looking code, defining functions, types, classes, etc, but usually without a main(), because the library does not do anything by itself. It just provides functions, types, classes, etc.

    and how you know what is in each and suchlike.
    That's what the header files are for; they contain function prototypes, type declarations, etc. The compiler needs that. As for the programmer, you can read the header (where they are depends on the system; on linux mostly /usr/include), but hopefully the library also has some more user friendly documentation.

    A library can have more than one header file. The C++ standard library could be organized a lot of different ways as determined by the OS design, but (AFAIK) it is usually just one big shared executable file (including the STL...?). Most of the time you are only using a subset of the available features, and you include the appropriate headers, eg:

    Code:
    #include <iostream>
    #include <string>
    Those are headers. There is not actually a "iostream" library, it is part of the C++ standard library. There's just the iostream header.

    You might want to read this thread from a few days ago too:

    header files
    Last edited by MK27; 09-21-2011 at 10:30 AM.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  4. #4
    Registered User
    Join Date
    Jan 2011
    Posts
    101
    Thanks Andrew and MK27, you have served to lighten my darkness considerably.

    I have bookmarked the reference detailing the C++ Library for future reference.

    This will probably sound simplistic but am I correct in assuming that somewhere, it shouldn'e really matter to me, inside my compiler I have a copy of the C++ Standard Library and when I use an 'include' statemant that is just telling the compiler to use a particlar part of that library.

    In fact much like I used to use libraries in BASIC, but I knew where they were and often had written them myself anyway.

    Onwards and upwards, it will slowly sink in..............

  5. #5
    spurious conceit MK27's Avatar
    Join Date
    Jul 2008
    Location
    segmentation fault
    Posts
    8,300
    Quote Originally Posted by JayCee++ View Post
    This will probably sound simplistic but am I correct in assuming that somewhere, it shouldn'e really matter to me, inside my compiler I have a copy of the C++ Standard Library
    No, it is not inside the compiler, because it is used by a lot of different programs concurrently. It's loaded into RAM when it is first required. On linux, if you type:

    lsof | grep stdc++

    You'll get a list of programs currently using the library and the path to its location.

    However, compilers and the standard library are very intimately related. I believe this generally means a normal compiler will only work with the standard library it was specifically built for (as in, the actual binary implementation, not "the C++ standard library" in general). Someone else may know more details about that.

    and when I use an 'include' statemant that is just telling the compiler to use a particlar part of that library.
    It's actually not telling it to use anything, it is just providing it with information so that it can use some part of the library properly if it needs to. Have at look at my post in that "headers" thread.

    In fact much like I used to use libraries in BASIC, but I knew where they were and often had written them myself anyway.
    This is a common practice in C/C++ too, I am sure you will get there soon enough. You can compile several source files together, only one of which has a main(); the others, transitionally, are compiled into object files which are like static libraries, then they are compiled into your exe. You can also compile a source file by itself as a shared/dynamic library, write a header for it, include that header in another program, and link to your shared library. Exactly how you do that is system/compiler dependent.
    Last edited by MK27; 09-21-2011 at 11:48 AM.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  6. #6
    Registered User
    Join Date
    Jan 2011
    Posts
    101
    Thanks for the extra clarification MK27 - I think we are both on the same page of the hymnsheet now even though we may not be in tune exactly!

  7. #7
    Registered User
    Join Date
    May 2009
    Posts
    2,613
    Quote Originally Posted by AndrewHunter View Post
    No, problem let's just get some terminology down. First, Code::Blocks is an IDE, not a compiler. Take a read through What is a compiler? ...
    Can this be rewritten
    Code::Blocks and MINGW Our recommended free compiler setup! Code::Blocks is also available on Linux.
    To something like this
    MINGW compiler with Code::Blocks IDE, Our recommended free compiler setup! Code::Blocks is also available on Linux.
    or this
    Code::Blocks IDE with MINGW Compiler, Our recommended free compiler setup! Code::Blocks is also available on Linux.

    Tim S.
    Last edited by stahta01; 09-21-2011 at 12:30 PM.

  8. #8
    Registered User
    Join Date
    May 2011
    Location
    Around 8.3 light-minutes from the Sun
    Posts
    1,866
    Quote Originally Posted by stahta01 View Post
    Can this be rewritten ....
    Disregard, I see what you mean. Yes I think one of those options would be better.
    Quote Originally Posted by anduril462 View Post
    Now, please, for the love of all things good and holy, think about what you're doing! Don't just run around willy-nilly, coding like a drunk two-year-old....
    Quote Originally Posted by quzah View Post
    ..... Just don't be surprised when I say you aren't using standard C anymore, and as such,are off in your own little universe that I will completely disregard.
    Warning: Some or all of my posted code may be non-standard and as such should not be used and in no case looked at.

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Which Libraries for SDL??
    By beginner in forum Game Programming
    Replies: 4
    Last Post: 02-19-2003, 06:35 PM
  2. libraries
    By Klinerr1 in forum C++ Programming
    Replies: 11
    Last Post: 07-30-2002, 04:53 AM
  3. libraries
    By Unregistered in forum C++ Programming
    Replies: 1
    Last Post: 07-26-2002, 02:12 PM
  4. bad libraries or what?
    By Paninaro in forum C Programming
    Replies: 3
    Last Post: 06-20-2002, 07:15 PM
  5. Libraries!!
    By Paninaro in forum C Programming
    Replies: 1
    Last Post: 06-20-2002, 12:07 AM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21