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cmakeeigeneigen3

cmake find_package unable to find Eigen3Config.cmake spectra Windows

I am using Eigen3 with spectra (https://spectralib.org/), a library built on top of Eigen. Spectra uses find_package to find Eigen, and comes up with the error:

 Could not find a package configuration file provided by "Eigen3" with any
  of the following names:

    Eigen3Config.cmake
    eigen3-config.cmake

Looking through the directory of Eigen, I found that there were no files by those names, but rather one called Eigen3Config.cmake.in. I tried copying the file and renaming it Eigen3Config.cmake, but that gave me a different error of 

find_package Error reading CMake code from "C:/Program Files
  (x86)/Eigen3/cmake/Eigen3Config.cmake".

which was somewhat expected, but it does tell me that it can at least find the directory where Eigen3Config.cmake.in is. I'm assuming that either find_package is supposed to use Eigen3Config.cmake.in, or Eigen3Config.cmake.in is supposed to generate Eigen3Config.cmake, but i'm very new to cmake, so i'm not sure. How do I fix this?

Solution

  • There is no need to build/install Eigen to use it if you include it manually, as done in the getting started example (https://eigen.tuxfamily.org/dox/GettingStarted.html#title0)

    But in order to be found by CMake, you will need to build / install it, as explained in the INSTALL file. https://gitlab.com/libeigen/eigen/-/blob/master/INSTALL

    Usually, your error is followed by an hint asking you to set the variable Eigen3_DIR (or something similar) to point the build/install dir of the target project (Eigen3 here). It appears typically when you have built but not installed the project.

    So:

    1. Build Eigen
    2. Install it (optional)
    3. For spectra set the cmake var Eigen3_DIR to /path/to/Eigen/build . (if eigen not install or still not found)