VXL-users Frequently Asked Questions


  1. I have successfully built VXL under MS Visual Studio, and am now trying to build a simple program that uses the libraries. The Linker complains that there are multiple definitions (error LNK2005) of several things from the C++ Standard Library. What is going wrong?

    These kinds of errors often indicate that you are linking against different C++ run-time libraries that you compiled VXL with (release vs debug, static vs DLL stdlib, etc). The flags like /MP and /MD much match exactly, in VXL's build and your program's build. These flags are set in Visual Studio under Settings->C/C++->Code Generation->Use run-time library.
    The easiest way to link against these projects, we've found, is to use CMake for your project too. CMake will then make sure the flags match, or else will give you an error or warning.


  2. I followed the VXL installation documentation, but found that the configuration output and/or entries in the CMakeCache.txt file say that CMake could not find programs, paths, etc. Is this a problem?

    No. VXL needs very little to build correctly (only a C/C++ compiler at worst), however it can make use of various system provided libraries, rather than build its own versions. CMake also looks for lots of system tools so that it can understand the environment it is in. So having lots of NOTFOUND entries, or "Could NOT find" reports is quite normal. There is no need to worry unless CMake displays a warning or error message while it runs.


  3. I used CMake to create a MSVC project with BUILD_SHARED_LIBRARY=ON. But when I try to build, it gives message "cannot open vcl.lib". What's wrong?

    VXL does not support the CMake "Shared Library" feature on MSVC. You have to use static libraries. This is mostly due to MSVC's requirements to have either a complete list of every exportable identifier or a decoration of every identifier in the code. We are too lazy (or appalled at this "feature") to try to fix this. If you absolutely need DLLs you can build your code using Cygwin, which can produce shared libraries in a "normal" manner. Alternatively, if you only want to export a small number of classes or functions, then you can manually list them. See the MSVC tool documentation for further details.


  4. I have successfully built VXL, but when I try to write my own program to use it, I get errors like "include file not found", or "unresolved symbol" , or "unresolved external symbol". What's wrong?

    Your makefile or IDE settings have not been correctly set up to include VXL .h files, or link against VXL or system libraries. Details can be found in the "Build Systems" appendix of the VXL Book. If you still have problems, show the appendix to a competent local programmer, and ask for their advice.


  5. I'm trying to compile the whole of VXL and I get compiler or linker errors in $VXL_SRC/XXX/YYY mentioning library ZZZ

    In many cases the code in question will be trying to use a system provided library ZZZ. You can tell VXL to not use that library by looking in your CMakeCache.txt file for references to ZZZ (e.g. ZZZ_LIBRARY or ZZZ_INCLUDE_PATH) and setting them to IGNORE. Alternative you can disable the building of some parts of VXL (e.g. all of YYY) by looking in your CMakeCache.txt file for references to BUILD_YYY, and setting them to OFF.


  6. No-one has answered my question on vxl-users. It is really important that I get an answer.

    Your questions may be very poorly posed, and none of the other members of vxl-users, can answer it. If you still haven't had a reply after a week, please read the vxl-users list policy, and repost your email after taking account of the advice in the policy.



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