Difference between static and shared libraries

Question

What is the difference between static and shared libraries   I use Eclipse and there are several project types including Static Libraries and Shared Libraries  Does one have an advantage over the other

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A static library is like a bookstore  and a shared library is like    a library  With the former  you get your own copy of the book function to take home  with the latter you and everyone else go to the library to use the same book function  So anyone who wants to use the  shared  library needs to know where it is  because you have to  go get  the book function  With a static library  the book function is yours to own  and you keep it within your home program  and once you have it you don t care where or when you got it

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For  a static library  the code is extracted from the library by the linker and used to build the the final executable at the point you compile build your application  The final executable has no dependencies on the library at run time  For a shared library  the compiler linker checks that the names you link with exist in the library when the application is built  but doesn t move their code into the application  At run time  the shared library must be available   The C programming language itself has no concept of either static or shared libraries - they are completely an implementation feature   Personally  I much prefer to use static libraries  as it makes software distribution simpler  However  this is an opinion over which much  figurative  blood has been shed in the past

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On top of all the other answers  one thing not mentionned yet is decoupling    Let me speak about a  real world production code that I have been dealing with    A very big software  made of  300 projects  with visual studio   mostly build as static lib and finally all link together in one huge executable    you end up with the following problems    -Link time is extremely long  You might end up by more than 15min of link  for let s say 10s of compilation time -Some tools are on their knee with such a big executable   like memory check tools that must instrument the code  You might fall into reaching limits that had been seen as fools   More problematic is the decoupling of your software   on this real world example  headers files of every project were reacheable from any others projects  As a consequence it was extremely easy for one developer to add dependencies  it was just about including the header  because link at the end will allwaws find symbols  It ends up by horrible cycling dependencies and complete mess   With shared library  it s a bit of extra work because developer must edit the project build system to add the dependent library   I observed that shared library code tends to offer a cleaner code API

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-------------------------------------------------------------------------     -       Shared dynamic            Static Library  Linkages            -------------------------------------------------------------------------  Pros    less memory use              an executable  using own libraries                                           coming with the program                                                doesn t need to worry about its                                           compilebility subject to libraries  -------------------------------------------------------------------------  Cons    implementations of           bigger memory uses                           libraries may be altered                                                  subject to OS  and its                                                    version  which may affect                                                 the compilebility and                                                     runnability of the code                                          -------------------------------------------------------------------------

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The most significant advantage of shared libraries is that there is only one copy of code loaded in memory  no matter how many processes are using the library  For static libraries each process gets its own copy of the code  This can lead to significant memory wastage   OTOH  a advantage of static libraries is that everything is bundled into your application  So you don t have to worry that the client will have the right library  and version  available on their system

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Shared libraries are  so  or in Windows  dll  or in OS X  dylib  files  All the code relating to the library is in this file  and it is referenced by programs using it at run-time  A program using a shared library only makes reference to the code that it uses in the shared library   Static libraries are  a  or in Windows  lib  files  All the code relating to the library is in this file  and it is directly linked into the program at compile time  A program using a static library takes copies of the code that it uses from the static library and makes it part of the program   Windows also has  lib files which are used to reference  dll files  but they act the same way as the first one    There are advantages and disadvantages in each method    Shared libraries reduce the amount of code that is duplicated in each program that makes use of the library  keeping the binaries small  It also allows you to replace the shared object with one that is functionally equivalent  but may have added performance benefits without needing to recompile the program that makes use of it  Shared libraries will  however have a small additional cost for the execution of the functions as well as a run-time loading cost as all the symbols in the library need to be connected to the things they use  Additionally  shared libraries can be loaded into an application at run-time  which is the general mechanism for implementing binary plug-in systems  Static libraries increase the overall size of the binary  but it means that you don t need to carry along a copy of the library that is being used  As the code is connected at compile time there are not any additional run-time loading costs  The code is simply there    Personally  I prefer shared libraries  but use static libraries when needing to ensure that the binary does not have many external dependencies that may be difficult to meet  such as specific versions of the C   standard library or specific versions of the Boost C   library

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Simplified    Static linking  one large executable Dynamic linking  a small executable plus one or more library files   dll files on Windows   so on Linux  or  dylib on macOS

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Static libraries are compiled as part of an application  whereas shared libraries are not  When you distribute an application that depends on shared libaries  the libraries  eg  dll s on MS Windows need to be installed   The advantage of static libraries is that there are no dependencies required for the user running the application - e g  they don t have to upgrade their DLL of whatever  The disadvantage is that your application is larger in size because you are shipping it with all the libraries it needs   As well as leading to smaller applications  shared libraries offer the user the ability to use their own  perhaps better version of the libraries rather than relying on one that s part of the application

[c++] Difference between static and shared libraries?

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