cmake:missing and no known rule to make it when I import a prebuilt library

Question

I want to import a prebuilt library using this CmakeLists.txt snippet:

add_library(openssl-crypto             SHARED             IMPORTED ) set_target_properties(openssl-crypto                       PROPERTIES                       IMPORTED_LOCATION                       ${external_DIR}/libs/${ANDROID_ABI}/libcrypto.so ) include_directories(${external_DIR}/include/openssl) 

I linked this to my library as:

target_link_libraries(aes-crypto openssl-crypto)

Attempting to build returns this error:

'/libs/arm64-v8a/libcrypto.so', needed by ...,  missing and no known rule to make it 

Answer 1

I found that the IMPORTED_LOCATION property, when passed to the set_target_properties function doesn't like relative paths.

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From the CMake Documentation on IMPORTED_LOCATION

Full path to the main file on disk for an IMPORTED target.

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To resolve this issue, I used the full path to the library instead.

Example:

set_target_properties ( curl-lib                          PROPERTIES IMPORTED_LOCATION                          libs/${ANDROID_ABI}/libcurl.a )  . . . becomes . . .   set_target_properties ( curl-lib                          PROPERTIES IMPORTED_LOCATION                          ${PROJECT_SOURCE_DIR}/src/main/cpp/libs/${ANDROID_ABI}/libcurl.a ) 

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The path to the library may differ slightly for you from the one above, but ${PROJECT_SOURCE_DIR} is normally a good starting point as it is defined as:

...the source directory of the last call to the project() command made in the current directory scope or one of its parents. Note, it is not affected by calls to project() made within a child directory scope (i.e. from within a call to add_subdirectory() from the current scope).