Eclipse IDE GCC linker options ?

Jochen Arndt

When passing library file names using the -l option strip of the lib prefix and the extension. If for example the file name is libcv2.so, pass -lcv2 as option. See Link Options - Using the GNU Compiler Collection (GCC)[^]. If the library file does not match this style (lib prefix, .a or .so extension, or you want to link dynamically to a .so file but there is also a matching .a file), you can pass the full name with path as argument like for object files (gcc recognises if the file is an object file or a libray). I can't help much regarding Eclipse. But a quick search shows that there are two different sections where you can configure libraries:

The general library settings (C/C++ Properties - Folder - General - Paths and Symbols)
The project and tool specific settings (C/C++ Properties - Project - Build - Settings - Tool Settings - Linker)

The first should be used for system wide general library paths while the second is for project specific settings. To add an object or library with full path and name, enter it at Miscellaneous - Other objects.

leon de boer

Jochen gave a full detail but I am going reduce his answer down to make it simpler gcc -l sets a library file name to link (we are assuming the file is in the library directory chains). gcc -L Sets the directory for library files. So the little l is a library file name (so it will be -l cv2 in your case), it's a simple name no folder, no extension. cv2.so is a shared object file so if the linker can't find it and it's there ... then your big L setting is wrong. So your big L should be -L /usr/local/lib Look at the command Eclipse fires out onto the command line and look for those two.

In vino veritas

Vaclav_

Thanks to all, I really appreciate your help. I did some more messing around and managed to input correct -L using / copying stuff affecting ALL projects. It sort off worked. Than I did -l and typed cv2.so and the linker could not find it. I'll try just cv2 without the so extension next. AS I said , there is an GUI option to select "shared" files so as soon as I can get the linker to work I'll play with that. I just rebuild another "buidl" using CMake again and will see what I messed up this time. I'll cannot post the linker output until I have it back working after this new Make, sorry.

Vaclav_

Here is what I am getting, I need to find out what /ld is , maybe that will give me a clue. And here is a terrible though - how do I verify that OpenCV will work on Unbutu - 32 bits and Eclipse - also 32 bits? I can run "hello world", but cannot get the linker to work with OpenCV. **** Build of configuration Debug for project TEST_1 **** **** Internal Builder is used for build **** g++ -L/usr/local/lib -shared -L/media/jim/OpenCL/OpenCV/build/lib -shared -olibTEST_1 src/TEST_1.o -l/cv2 -l/cv2.so -l/media/jim/OpenCL/OpenCV/build/lib/libopencv_flann_pch_dephelp.a -l/media/jim/OpenCL/OpenCV/build/lib/libopencv_videoio.so -l/media/jim/OpenCL/OpenCV/build/lib/libopencv_videoio -llibopencv_videoio /usr/bin/ld: cannot find -l/cv2 /usr/bin/ld: cannot find -l/cv2.so /usr/bin/ld: cannot find -l/media/jim/OpenCL/OpenCV/build/lib/libopencv_flann_pch_dephelp.a /usr/bin/ld: cannot find -l/media/jim/OpenCL/OpenCV/build/lib/libopencv_videoio.so /usr/bin/ld: cannot find -l/media/jim/OpenCL/OpenCV/build/lib/libopencv_videoio /usr/bin/ld: cannot find -llibopencv_videoio collect2: error: ld returned 1 exit status Build error occurred, build is stopped Time consumed: 186 ms.

leon de boer

You only need one of these for cv2

-l/cv2 -l/cv2.so

but as neither is working, try fully qualifying it as a single entry which means use a colon

-l:cv2.so

The reason I think you are having to do that is you have not set GCC command with the -shared cv2.so if you look you have -shared and nothing after it You have can set the -L directory I don't think the -l command can have directory entries :-)

-L/my/long/directory -lfoo -L/my/other/even/longer/directory -lfoo1

That I believe is how you do library foo & foo1 from different long directories Edit: I also see above you got the make file sort of working so you must be able to see the actual command lines to the linker.

In vino veritas

Lost User

ld is the linker which collects all the object modules and libraries, and combines them into a new library, or an executable program. The library options to the linker are as follows: -L followed by a directory path, adds that directory to the list of locations to be searched for any additional libraries. -l add the undecorated library name to the list of libraries required by the object code. Note that libraries are commonly held in files which are named liblibraryname**.suffix**, where suffix is .a or .so. However the name specified on the option line should just be libraryname, i.e. no preceing lib and no suffix. And no directory paths. So the options you should be using for /media/jim/OpenCL/OpenCV/build/lib/libopencv_flann_pch_dephelp.a should be something like:

-L/media/jim/OpenCL/OpenCV/build/lib
-lopencv_flann_pch_dephelp

And it would really make your questions easier to read if you would use <pre> tags as requested many times.

Vaclav_

Good news, it linked AFTER I changed the -l to -l:cv2.so I'll check the GCC linker -l option and try to figure it out. It seems I should not have to add the .so extension to the file name. But it would not work without it, probably related to -shared option too. As far as the -shared - it is a common option and I need to find out how it works too. I beginning to believe the Elipse Settings GUI is not telling the whole story as far as how to use it. There is "Common" window dialog of all the options currently set , but it cannot be edited !

Jochen Arndt

To nail it down again: The -l option requires a stripped library name without path, lib prefix, and extension! When specifying all library pathes with the -L option, it must be just:

-lcv2
-lopencv_flann_pch_dephelp
-lopencv_videoio

The linker (ld) will then search all directories specified with the -L option for matching files by building the full name from the path actually searched, appending the lib prefix, appending the name passed to the -l option, and appending the extension .a. If that fails for a path, it tries again with the extension .so.

Vaclav_

Yes, that is how is SHOULD work per GCC linker.

leon de boer

Yeah sorry I can't help with Eclipse I just put GCC on my external tools menu on Visual Studio 2015 :-) I am too slack to learn another IDE.

In vino veritas

Lost User

And that is how it does work. You just need to ensure that your options and parameters are specified correctly.