Why does linker fail to resolve dependencies within the same .a file?

Nick Clifton nickc@redhat.com
Wed Feb 28 09:57:00 GMT 2007


Hi Christian,

> /usr/bin/c++ -fPIC "CMakeFiles/simpleIO.dir/main_IO.o" -o
> simpleIO -rdynamic
> -L/home/cjc/csc583-svn/uriVisionLib/trunk/Development/Source/C++ -lGL
> -lglut -Wl,-Bstatic -luriVision -luriVision -Wl,-Bdynamic
> -Wl,-rpath,/home/cjc/csc583-svn/uriVisionLib/trunk/Development/Source/C++

Note: Placing "-luriVision" twice on the command line next to each other 
like that will not actually gain you anything.  The only reason to 
include a library more than once on a linker command line is if it 
contains symbols that are referenced by files that are placed after the 
first occurrence of the library on the command line.  eg:

   foo.o -lbar baz.o -lbar

The second "-lbar" is only needed if baz.o includes references to 
symbols that are defined in libbar.a which will not be pulled in when 
resolving the references made by foo.o.

> In function `uriVideoSources::ImageReader::getFrame(bool,
> uriBase::RasterImage*)':
> ImageReader.cpp:(.text+0x90): undefined reference to
> `uriVideoSources::ImageReader_gen::getFrame_(bool,
> uriBase::RasterImage*)'

> cjc@peace:~$ nm --demangle
> /home/cjc/csc583-svn/uriVisionLib/trunk/Development/Source/C++/liburiVision.a 
> | grep outputFrame

As has already been pointed out you are greping for 'outputFrame' when 
the error message you have reported was for a missing 'getFrame_' 
symbol.  I assume therefore that you are also getting error messages 
about a missing reference to 'outputFrame_' ?

> 0000002c T uriMovieEditing::ImageWriter::outputFrame(uriBase::RasterImage*)
> 00000000 T uriMovieEditing::ImageWriter::outputFrame(uriBase::RasterImage*,
> bool)
>        U 
> uriMovieEditing::ImageWriter_gen::outputFrame_(uriBase::RasterImage*,
> bool)

Which if the above assumption is correct means that the linker is right. 
   uriMovieEditing does contain an unresolved reference to an 
outputFrame_ symbol.  You will need to add whichever library or object 
file contains that symbol to the linker command line, and if it is a 
library that contains it, then it must come *after* -luriVision on the 
command line.

Cheers
   Nick



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