Let me explain my problem: I wrote a shared library libMyLib.so that uses OpenCV libopencv_core.so.
When I write an application that uses my library (libMyLib.so) I would like to hide the use of OpenCV library (i.e. an implicit link) but I'm not able. I have to link explicitly to libopencv_core.so too.
What should I do? Is it possible or I have to link OpenCV statically to my own library to hide it?
I'm using NetBeans 7.3.1 with gcc 4.7.3 and ld 2.23.2.
Thanks for your help!
It should be possible to link the OpenCV library statically. I don't think there's much that can be done to completely hide the OpenCV library symbols in a process that loads the shared library. The following options to ld should work:
ld ... -static -lopencv_core -Bdynamic ...
If calling from cc, then it's like this:
gcc ... -Wl,-static,-lopencv_core,-Bdynamic ...
Another possibility is using dynamic loading of the library with dlopen() and finding symbols with dlsym(). This may work to hide the rest of the library's symbols. Here's an online version of the manpage for those: http://linux.die.net/man/3/dlopen.
Related
I'm using Mingw32 compiler to build a C++ app.
I'm passing -nostdlib to the linker because I only want to link the libraries I'm going to actually use.
However I'm running into a problem with the C++ standard library.
When I link with libstdc++ I get the following error:
undefined reference to '_Unwind_SjLj_Register'
So clearly libstdc++ isn't the right library to link with.
Is there any way of seeing what libraries Mingw32 links with by default when building a C++ app?
What libraries are being excluded when the flag -nostdlib is passed to linker?
Thanks.
I have downloaded the OpenSSL binary file. I would like to create a static library for my C++ program in Ubuntu.
Meaning that they are in the same directory.
http://www.openssl.org/source/
Add -static parameter to gcc when you are linking. I expect you want to static binary without any dynamic loaded libraries. In other case, add full path to libssl.a as object file to linking in your build system. You have not specified how are you going to build your application.
Manually, you would use something like:
gcc -o application yourcode.c yourcode2.c /usr/lib/libssl.a
or better
gcc -static -o application yourcode.c yourcode2.c -lssl
Downloading binary for Linux is bad idea in most cases. If you want static binary, this should help. If you need custom build of library with special features, you need to download and build that library from sources yourself.
Anyway, similar question to yours is answered here at Static link of shared library function in gcc
You might also check Linux static linking is dead? to discover there are maybe too many problems to even consider static linking.
And if you need more information about linking under Linux, check nice tutorial at http://www.yolinux.com/TUTORIALS/LibraryArchives-StaticAndDynamic.html
I am writing a library that is loaded dynamically by another progam. This library uses some Boost libraries (for example, thread). Is it possible to make it work somehow without recompiling the program in question?
If I use the link flags -lboost_thread, it doesn't work, because the program that uses this library would need to link the same Boost library, too. Using /usr/lib/libboost_thread.a also doesn't work, because the .a file isn't compiled with -fPIC.
I am using GCC under Linux.
Trying again, I found that the problem was not what I described. The library didn't load for some other reason. I found that linking the library with -lboost_thread works, with the following conditions:
gcc gives compiler warnings (possibly because the libraries are from the -L path which is not in $LD_LIBRARY_PATH).
When loading the library, it loads Boost automatically provided it can find them.
First, I don't know if there is a solution to my problem at all.
I have the following situation:
I have developed a framework library that depends on several other libraries for specific hardware access, etc.
Until now this framework library was only statically linked against.
For the executable that uses the framework library only the dependencies of code that is actually used by the executable have to be linked. (If I don't access a specific hardware at all I don't have to depend on its associated libraries.)
Now I need to also make a shared object of the framework library. Also the dependencies are available as shared libraries, so there is no need for any static linking.
The problem I have now:
When building an application that links dynamically to the framework library I have to either link all dependencies dynamically to the framework library or the application. (Otherwise I get undefined references complaints from ld)
My questions:
Is there any way to ignore certain shared object dependencies if I know that my application will not use any code of the framework library that depends on this shared object?
Is there any way to do this without or with minimal code changes? (linker / compiler switches)
I also need the static linking as described in the original situation to still work.
Additional Info:
Operating system: Linux (Debian Lenny)
Compiler: gcc-4.3
You can, but you basically have to do all of the dynamic library handling yourself. i.e. dlopen the library, and then look up the symbols you need directly with dlsym.
It will make your code more complicated, how much depends on the interface you've got into the libraries.
From man ld
--as-needed
--no-as-needed
This option affects ELF DT_NEEDED tags for dynamic libraries mentioned on the command line after the --as-needed option. Normally,
the linker will add a DT_NEEDED tag for each dynamic library mentioned on the command line, regardless of whether the library is
actually needed. --as-needed causes a DT_NEEDED tag to only be emitted for a library that satisfies a symbol reference from regular
objects which is undefined at the point that the library was linked, or, if the library is not found in the DT_NEEDED lists of other
libraries linked up to that point, a reference from another dynamic library. --no-as-needed restores the default behaviour.
I haven't used it myself but sounds like what you're looking for.
g++ -o your_app -Wl,--as-needed -lframework -la -lb -lc -Wl,--no-as-needed
Edit (suggested by Hanno)
--warn-unresolved-symbols
If the linker is going to report an unresolved symbol (see the option --unresolved-symbols) it will normally generate an error.
This option makes it generate a warning instead.
I have a problem linking boost.asio. It uses boost.system and the linker errors start with:
/boost_1_39_0/boost/system/error_code.hpp:205: undefined reference to `boost::system::get_system_category()'
which means I need to link boost.system. I already built boost and I have now several lib files.
boost_system-mgw32-d-1_39.dll and lib
libboost_system-mgw34-d-1_39.lib
libboost_system-mgw34-mt-d-1_39.lib
libboost_system-mgw34-sd-1_39.lib
and some more. How do I link them? Which one do I use? Do I copy all of them together?
My system is win32+mingw+eclipse cdt+qt 4.5.2+qt integration for eclipse. I already learned that I need to at a LIBS= section to my .pro file.
Can you give my some hints?
Thank you.
The libraries are named based on whether or not multi-threading support is enabled, static and dynamic linkage, debug and release mode, and more. Here's some details:
http://www.boost.org/doc/libs/1_39_0/more/getting_started/unix-variants.html#library-naming
I'm not sure about eclipse as I don't use it, but with gcc (and mingw) you need to specify both a directory to find the libraries in (-L) and the file to link with. For example, if you wanted to link with the single-threaded debug version:
-L/path/to/libraries -lboost_system-mgw34-sd-1_39