We will reuse the C++ example from Chapter 3, Detecting External Libraries and Programs, Recipe 4, Detecting the BLAS and LAPACK math libraries, to illustrate the use of the first variant of add_custom_command. In that code sample, we probed for existing BLAS and LAPACK libraries and compiled a tiny C++ wrapper library to call the Fortran implementation of the linear algebra routines we needed.

We will split the code into two portions. The source file for linear-algebra.cpp is unchanged compared to Chapter 3, Detecting External Libraries and Programs, Recipe 4, Detecting the BLAS and LAPACK math libraries, and will include headers from the linear algebra wrappers library and link against the compiled library. The sources of the library will, however, be packaged into a zipped tar archive shipped alongside the example project. The archive will be extracted at build time and the linear algebra wrapper library compiled before the executable.