Use cmake FindBLAS to link OpenBLAS

Question

I am using cmake 3.16, and I know that cmake supports finding OpenBLAS by using FindBLAS (here).

I am trying to link OpenBLAS to my c++ project. Here is my CMakeLists.txt.

cmake_minimum_required(VERSION 3.15)

project(my_project)

# source file
file(GLOB SOURCES "src/*.cpp")

# executable file
add_executable(main.exe ${SOURCES})

# link openblas
set(BLA_VENDER OpenBLAS)
find_package(BLAS REQUIRED)
if(BLAS_FOUND)
    message("OpenBLAS found.")
    include_directories(${BLAS_INCLUDE_DIRS})
    target_link_libraries(main.exe ${BLAS_LIBRARIES})
endif(BLAS_FOUND)

If I run cmake, it runs just find, and outputs OpenBLAS found.. However, if I start to compile the codes (make VERBOSE=1), the library is not linked, so that the codes fail to compile. Here is the error info:

fatal error: cblas.h: No such file or directory
 #include <cblas.h>
          ^~~~~~~~~
compilation terminated.

I installed OpenBLAS successfully. The header files are in /opt/OpenBLAS/include, and the shared libraries are in /opt/OpenBLAS/lib. My OS is ubuntu 18.04.

Any help? Thank you!

Description "so that the codes fail to compile" is not helpful. Please, provide **exact** error message you got. Also, using `message()` command you may print values of variables which you use (`BLAS_INCLUDE_DIRS` and `BLAS_LIBRARIES`). BTW, the first variable - `BLAS_INCLUDE_DIRS` - is not noted in the documentation you refer to. — Tsyvarev, Dec 31 '19 at 23:05

score 0 · Accepted Answer · answered Jan 03 '20 at 15:10

Thanks Tsyvarev. I found the problem.

I tried to use message() to print out the variables.

message(${BLAS_LIBRARIES})

Which gives:

/opt/OpenBLAS/lib/libopenblas.so

So the shared library is found.

However, for BLAS_INCLUDE_DIRS, it gives:

message(${BLAS_INCLUDE_DIRS})
CMake Error at CMakeLists.txt:27 (message):
  message called with incorrect number of arguments

It turns out that BLAS_INCLUDE_DIRS is not in the FindBLAS variables. So I add the include header files manually:

set(BLA_VENDER OpenBLAS)
find_package(BLAS REQUIRED)
if(BLAS_FOUND)
    message("OpenBLAS found.")
    include_directories(/opt/OpenBLAS/include/)
    target_link_libraries(main.exe ${BLAS_LIBRARIES})
endif(BLAS_FOUND)

This time it compiles without error. Instead of using include_directories(), you could also try find_path() (check this).

Use cmake FindBLAS to link OpenBLAS

1 Answers1