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Help pls...linking to a lib is not working [message #1716209]

Wed, 02 December 2015 08:56

ingo stein

Messages: 1
Registered: December 2015

Junior Member

Hey guys...
I don't get it....
I want to use the Myo64.lib from the Myo Wristband but i'm not able (or maybe just to sutpid) to set up the program correctly.

The code is just a sample and the error does not look like an code-error.
So this is my error i'm getting:

09:43:00 **** Incremental Build of configuration Debug for project Myo_Tests ****
Info: Internal Builder is used for build
g++ "-LC:\\Users\\Computer\\workspace\\Myo_Tests\\libs" -o Myo_Tests.exe "src\\hello-myo.o" -lmyo64.lib 
c:/mingw/bin/../lib/gcc/mingw32/4.8.1/../../../../mingw32/bin/ld.exe: cannot find -lmyo64.lib
collect2.exe: error: ld returned 1 exit status

09:43:00 Build Finished (took 236ms)

I set the System Pathvariable to
C:/MinGW/bin

the libraries to
Myo64.lib

the Library Path to
/$(ProjName)/libs

and ofc the Myo64.lib is existing in this project folder

If anyone could help me,this would be awesome^^
Thank you!

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Re: Help pls...linking to a lib is not working [message #1716289 is a reply to message #1716209]

Wed, 02 December 2015 17:22

David Vavra

Messages: 1426
Registered: October 2012

Senior Member

According to the GNU ld documentation -lxxx is converted to libxxx.so or libxxxx.a so it is looking for libmyo64.lib.a or libmyo64.lib.so in your case.
https://ftp.gnu.org/old-gnu/Manuals/ld-2.9.1/html_node/ld_3.html
I haven't built anything for Windows for some time but one way around this is to just put the full path to the library as a file to be linked without any preceding -l. This may drag in the entire library.

Here is some specific documentation at MinGW for linking libraries
http://www.mingw.org/wiki/specify_the_libraries_for_the_linker_to_use

And according to it:
if you have a library named according to the aberrant "lib<name>.lib" convention, it will not be found by an "-l<name>" specification -- if you cannot rename the library, you must use the form "-llib<name>"

HTH

[Updated on: Wed, 02 December 2015 17:27]

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Re: Help pls...linking to a lib is not working [message #1716312 is a reply to message #1716209]

Wed, 02 December 2015 20:50

Tauno Voipio

Messages: 742
Registered: August 2014

Senior Member

Check the library capitalization: myo64.lib is different from Myo64.lib.

--

Tauno Voipio

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Re: Help pls...linking to a lib is not working [message #1716316 is a reply to message #1716312]

Wed, 02 December 2015 22:34

David Vavra

Messages: 1426
Registered: October 2012

Senior Member

FWIW:
I tried a project (HelloWorldC++) with an empty myo64.lib in directory libs.

I was unable to get the GNU loader to find it using the following command in the HelloWorldC++ project directory:
g++ HelloWorldC++.o -Llibs -lmyo64
g++ HelloWorldC++.o -o HelloWorldC++ -Llibs -llibmyo64
g++ HelloWorldC++.o -Llibs -llibmyo64.lib

All of the above resulted in ld: cannot find ....

It did finally work when I used:
g++ HelloWorldC++.o -o HelloWorldC++ libs/libmyo64.lib
although I got: libs/libmyo64.lib: file not recognized: File truncated
but I expected this because the file is empty.

It seems the only way to get the library is to explicitly place it on the command line as if it were an object file.
According to the e ld documentation the only difference between -lNAM and /pathtolibs/libNAM.a is that -l surrounds NAM appropriately.
It's not clear though if a file without .a or .so will be treated as a library.

Previously I had linked to an older version of the ld manual.
The newer one is https://gcc.gnu.org/onlinedocs/gcc/Link-Options.html

Although Windows files aren't case sensitive, some linux commands still have case sensitive file searches. So, as Tauno suggests, use the proper case in the name to be sure.

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