CODEWITHSUNDEEP
cmake
user10140749
user10140749

Reputation:

CMake set variable

In the following CMake code snippet, I am confused by the if elseif check. My understanding is that BL will always be "Ei", so there is no need to check other values. Are there any scenarios where BL could be overwritten by something else? I am new to CMake so need some help here. 

set(BL "Ei" CACHE STRING "library")
set_property(CACHE BL PROPERTY STRINGS "Ei;AT;Op")
message(STATUS "The backend of choice:" ${BL})
if(BL STREQUAL "Ei")
...
elseif(BL STREQUAL "AT")
...
elseif(BL STREQUAL "Op")
...
else()
message(FATAL_ERROR "Unrecognized option:" ${BL})
endif()

Upvotes: 1

Views: 2179

Answers (1)

Daniel Schepler
Daniel Schepler

Reputation: 3103

The code set(BL "Ei" CACHE STRING "library") defines a CMake cache variable. However, without a FORCE option in the set statement, that means that it will not be overwritten if the variable was previously defined in the cache.

One way for a user to set a different value for BL would be on the cmake command line. For example: cmake ../sourcedir -DBL:STRING=AT

By entering the variable in the cache as type STRING (as opposed to type INTERNAL) that also makes the variable available to be configured in cmake-gui or in ccmake. (Furthermore, the set_property(... STRINGS ...) directive tells cmake-gui to produce a drop-down list containing Ei, AT, and Op to select from. However, this isn't enforced for setting the variable from the command line, which is why it's still a good idea to have the default case signalling an error.)

See the section "Set Cache Entry" under CMake's documentation for set for more information.

Upvotes: 1

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