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:
Using the command line--> apt-get install library
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...?
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).
Related
I want some basic explanation about how external libraries are added to a Qt C++ project in a Linux environment
I've installed a library called podofo in two ways :
- Installed it with apt-get install libpodofo
- Installed the source code and build it
Afterwards i added in the .pro file of my Qt Project : LIBS += -lpodofo
How do i choose whether he works with the first or the second one ?
How am i supposed to add an external library with a lot of .jar files in my project ?
I figured it might be something in the run environment but i still don't get it. I tried changing it but it seemed better to just copy libraries manually in the file Qt is installed in.
Like most libraries on Linux, podofo installs a pkg-config file. The file is named libpodofo-0.pc. qmake has built-in support for that, so all you need to do is add this to your project file:
PKGCONFIG += libpodofo-0
(Note that for this to work, you might need to add link_pkgconfig to your CONFIG line.)
Do not add anything to LIBS. qmake will call pkg-config and add the needed compiler and linker flags automatically. Specifically, it will add the correct -l flags for linking, and the correct -I flag for compiling (usually -I/usr/include/podofo). So when you include the podofo headers in your code, don't use #include <podofo/podofo.h>. Use #include <podofo.h> to keep your code portable when building on systems that might be using a different directory name to install the podofo headers.
Make sure that the pkg-config tool is actually installed on your system though. pkg-config --version should print something like 0.29.1. If instead the command is not found, then install the pkg-config package of your Linux distribution.
I'm trying to build wxWidgets library into a custom path on a Fedora 27 operative system.
I achieved the wx-config file path recognition and works with the cmake execution. Also, I load libraries and include dirs based on modified wxWidgets finder cmake file that sets thewx-config custom path successfully.
But cmake does not load my wxWidgets configuration. I mean, wx_gtk2u_jpeg-3.1 builded lib could not be founded (suposed to be /usr/lib/libwx_gtk2u_jpeg-3.1.so). I need jpeg dependency from wxWidgets for my project.
I'm sure that problem is not about cmake files. However, the problem is wxWidgets compilation because cmake can found the other builded dependencies into /usr/lib/
I actually installed the libjpeg-turbo-devel package that includes the libjpeg.h needed for wxWidgets building without success of libwx_gtk2u_jpeg-3.1.so creation.
The weirdest part is that $ wx-config --libs shows the wx_gtk2u_jpeg-3.1 lib to be linked and the hint paths that it should be founded.
wxWidgets commands for building:
$ ./configure --with-libjpeg=builtin --with-libpng=builtin --with-libtiff=builtin --with-zlib=builtin --with-expat=builtin --enable-webviewwebkit=no --prefix=/opt/cpp_dependencies/2018Q1/usr'
$ make -j 4
$ make install
You can check out my cmake files, the cmake output and wxWidgets building output in order to reproducing it: https://gist.github.com/jjalvarezl/b70accae269ef56c56010bedf157c27f
You can see line 1543 of wxWidgets building output file that jpeg library is buildin, and, 1564 of same file, the make install command that installs all libwx_<lib_name>.so libraries into final /usr/lib path. Anyway, no one contains the needed library.
Please show the exact error message, as it's not clear what the actual problem is. What I can say, is that the different built-in versions of 3rd party libraries, such as libjpeg, are always static libraries, even when wxWidgets themselves are shared. I.e. you're never going to have libwx_gtk2u_jpeg-3.1.so, only .a.
I'd also strongly recommend using system versions of the 3rd party libraries under Unix systems. This means that your wxWidgets applications will get security updates from your OS vendor and you don't risk running into any incompatibilities due to using 2 different versions of the same library in your application.
There are similar topics, but I haven't managed to find my answer in them.
I am building a test console application using the code::blocks IDE. It needs to load a DVB shared library called libhdhomerun.so (from Silicon Dust) for the HD Homerun DVB tuners. The HDHR tuner library has being installed using ./configure, ..., sudo make install, ldconfig etc and it all works with their utilities (built at the same time). So - the library is there and OK.
The library installed itself into /usr/local/lib. There is actually no symlink to it as there is with other shared libraries, but then it doesn't have any version information on the end either.
When I build the code (having explicitly included /usr/local/lib/libhdhomerun.so), the ld stage fails with
"cannot find -lhdhomerun.so"
I have tried every combination of including (/usr/local/lib/) libhdhomerun.so, hdhomerun.so, libhdhomerun, hdhomerun, creating a symlink to it etc. Nothing makes any difference.
The bizarre thing is that I have udev, mysql and libdvbv5 shared libraries included in exactly the same way, and they are fine. The only one that will not link is hdhomerun.
If I run a manual verbose link step from the command line "ld -lhdhomerun.so --verbose", it does fail - because it is trying to find libhdhomerun.so.so.
Any suggestions gratefully received - but I do need to keep using code::blocks.
To link the library properly, you need to have library path defined in your environment, and use proper library name with -l flag. Library path is defined in LD_LIBRARY_PATH environment variable. For -l flag to g++, library extension should not be provided - as you already observed, so in your case it should be like this:
-lhdhomerun
I'm wondering how to "package" a C++ project for release. It uses various libraries, and I don't want a user to have to go through the same setup I did, with putting the right files in the right place and such. I had difficulty researching this, because I'm not sure the technical term for this issue. If I'm using command line compiling on Linux, is there an easy way to do this?
Your approach to this will differ on Windows and Linux because each OS handles this a different way. I'm more familiar with Linux so I'll restrict my answer to just the Linux side of things.
When you link your executable with a library using -l flag the linker defaults to looking in the normal system library directories so there are four approaches here.
Require the user to properly install the libraries themselves. However, it sounds like you don't want to do that.
Have the user add the library location to LD_LIBRARY_PATH variable.
Your third option is force the linker to look in a certain path for the libraries using the -rpath flag. For example, to have the application look in its working directory for a shared library you can compile with: g++ -rpath ./ -l SomeLib -o MyApp myapp.cpp
One other option is to static link your code with their library that way you only have to distribute one executable. If a static library exists you can use g++ -static -l SomeLib -o MyApp myapp.cpp to tell gcc to link statically.
On windows I would recommand wix http://wix.sourceforge.net/ to create the .msi installer
I would like to point out, the lookup path for .dlls I recommand putting all .dll in the same folder as your .exe since this has the highest priority
However, the vc crt (the c/c++ runtime library) should be installed using the redistributional package from microsoft -> updates automatically http://www.microsoft.com/de-de/download/details.aspx?id=5555
Wix can include the redistributional package into the same .msi therefore you have only to deploy a single installer file.
You mean an installer?
On Windows the program that you run to install a new app which outs everything in the correct directory, creates the start menu and lets you un-install it?
There is an installer builder in Visual Studio (might not be in the free express version) which makes .msi installer files. It's fairly easy to use for simple tasks but becomes complicated to do anything more.
Alternatively, to create traditional setup.exe type installs I use the excellent free Innosetup
On linux you would generally create a package using whatever format your distribution uses (.deb / .rpm ). There are lots of instructions on the specifics of each one and the tools to do so will probably already be installed in your Linux system
I'm trying to implement soci in my program but I don't know how. I'm using C++ on Linux, on a project using netbeans. I have followed the steps in: http://soci.sourceforge.net/doc/structure.html to install it, and I tried to copy the files soci.h from /src/core and soci-mysql.h from /src/backends/mysql in my project but it gives a compilation error (these files include other soci files, but it's illogical to copy all files into the directory...). I have read the guide several time but I don't understand what I'm doing wrong. The examples only include these files.
Thanks.
Edit: I have given more information in a comment below the answer. I don't know what steps I have to follow to implement soci.
The relevant bit on that page is
When the configure script is run without parameters, the remaining part of the process will use /usr/local/include/soci as a default destination for SOCI header files and /usr/local/lib as a default destination for library files
Now /usr/local/include ought to be in your default include path (e.g. try something like gcc -c -v -x c++ /dev/null -o /dev/null to see the list your install uses) and so you can include these using
#include <soci/soci.h>
#include <soci/soci-mysql.h>
You then need to add the libraries to your link step. It looks like you'll have both static and shared versions of the libraries. You'll need to add -lsoci_core -lsoci_mysql to your link step; however if that doesn't work then you'll also need to specify /usr/local/lib as a search directory i.e. -L/usr/local/lib -lsoci_core -lsoci_mysql. (Again it's probably there already but you can see using gcc -print-search-dirs.) However, the issue then is that if you're using the shared version and /usr/local/lib isn't in your distributions library search path (see /etc/ld.so.conf and/or /etc/ld.so.conf.d/*) then it won't be able to find the shared library at runtime. You'll need to either hard-code in the path to the library with the linker switch -rpath or add /usr/local/lib to the system-wide search path as before or in your environment (variable LD_LIBRARY_PATH). I'm not sure what the best way to do this is - I'd suggest -rpath to avoid modifying the system in general, although if you're building a lot of libraries into /usr/local/lib it might make sense to add it.
I got the same doesn't load backend error on my C++ program when I execute session sql("mysql://db=...)
I found a solution (at least on my Ubuntu 11.04). Just do:
sudo -i ln -s /usr/lib/libsoci_mysql-gcc-3_0-3.0.0.so /usr/lib/libsoci_mysql.so
It seem that the SOCI library search for the file /usr/lib/libsoci_mysql.so that is not in the system, buy if you make a link to the library /usr/lib/libsoci_mysql-gcc-3_0-3.0.0.so that it's in the system it works (I think debian/ubuntu makes a file name change from the original name, but it have side effects because the SOCI library search inside for the original name).
I found the error using the bash environment variable LD_DEBUG=files and running my C++ binary.
Hope it helps.