External Dependencies

Source

13-external-dependencies/
├── bin
│   ├── CMakeLists.txt
│   ├── hello-first.cpp
│   ├── hello-second.cpp
│   └── hello-third.cpp
├── blacklist
│   ├── blacklist.cpp
│   ├── blacklist.h
│   └── CMakeLists.txt
├── CMakeLists.txt
├── DemoConfig.h.in
└── libhello
    ├── CMakeLists.txt
    ├── greeter-alias-db.cpp
    ├── greeter-alias-db.h
    ├── greeter.h
    ├── greeter-name.cpp
    ├── greeter-name.h
    ├── greeter-simple.cpp
    └── greeter-simple.h

• 13-external-dependencies/CMakeLists.txt

• 13-external-dependencies/DemoConfig.h.in

• 13-external-dependencies/bin/CMakeLists.txt

• 13-external-dependencies/bin/hello-first.cpp

• 13-external-dependencies/bin/hello-second.cpp

• 13-external-dependencies/bin/hello-third.cpp

• 13-external-dependencies/libhello/CMakeLists.txt

• 13-external-dependencies/libhello/greeter.h

• 13-external-dependencies/libhello/greeter-simple.h

• 13-external-dependencies/libhello/greeter-simple.cpp

• 13-external-dependencies/libhello/greeter-name.h

• 13-external-dependencies/libhello/greeter-name.cpp

• 13-external-dependencies/libhello/greeter-alias-db.h

• 13-external-dependencies/libhello/greeter-alias-db.cpp

• 13-external-dependencies/blacklist/CMakeLists.txt

• 13-external-dependencies/blacklist/blacklist.h

• 13-external-dependencies/blacklist/blacklist.cpp

FIND_PACKAGE()

Teacher’s note

$ sudo dnf remove sqlite-devel

Documentation

• FIND_PACKAGE()

• List of available “find” modules: cmake-modules(7)

• FindSQLite3

• Pulling in parameters for SQLite3

Toplevel CMakeLists.txt

FIND_PACKAGE(SQLite3)      # <--- continues if not found

$ cmake /home/jfasch/work/jfasch-home/trainings/material/soup/cmake/13-external-dependencies/
...
-- Could NOT find SQLite3 (missing: SQLite3_INCLUDE_DIR SQLite3_LIBRARY)
...

• ⟶ Handle through optional code (like in Optional Code, Approach 1: Optional blacklist, C Macro (Global Flags) and Optional Code, Approach 2: Pushing Optionality Down In Module Interface)

FIND_PACKAGE(... REQUIRED)

Note

A requirement appears to only fail if at least one target depends on the imported target

libhello/CMakeLists.txt

TARGET_LINK_LIBRARIES(hello SQLite::SQLite3)

• Requiring SQLite3 ⟶ failing if not found

  FIND_PACKAGE(SQLite3 REQUIRED)
  

  $ cmake /home/jfasch/work/jfasch-home/trainings/material/soup/cmake/13-external-dependencies/
  ...
  CMake Error at libhello/CMakeLists.txt:8 (TARGET_LINK_LIBRARIES):
    Target "hello" links to:
  
      SQLite::SQLite3
  
    but the target was not found.  Possible reasons include:
  
      * There is a typo in the target name.
      * A find_package call is missing for an IMPORTED target.
      * An ALIAS target is missing.
  

• Success after installing sqlite-devel

  $ sudo dnf install sqlite-devel
  $ cmake /home/jfasch/work/jfasch-home/trainings/material/soup/cmake/13-external-dependencies/
  ...
  -- Found SQLite3: /usr/include (found version "3.36.0")
  ...
  

SQLite3 Parameters

• Find-modules usually set variables

• FindSQLite3 is documented to set those (put in toplevel CMakeLists.txt)

  MESSAGE(DEBUG "SQLite3_INCLUDE_DIRS ${SQLite3_INCLUDE_DIRS}")
  MESSAGE(DEBUG "SQLite3_LIBRARIES ${SQLite3_LIBRARIES}")
  MESSAGE(DEBUG "SQLite3_VERSION ${SQLite3_VERSION}")
  MESSAGE(DEBUG "SQLite3_FOUND ${SQLite3_FOUND}")
  

  $ cmake --log-level=debug /home/jfasch/work/jfasch-home/trainings/material/soup/cmake/13-external-dependencies/
  ...
  -- SQLite3_INCLUDE_DIRS /usr/include
  -- SQLite3_LIBRARIES /usr/lib64/libsqlite3.so
  -- SQLite3_VERSION 3.36.0
  -- SQLite3_FOUND TRUE
  ...
  

Using SQLite3 Parameters

• With “Modern CMake” (that with targets, and propagated properties) not necessary anymore

• Used to be necessary in olden days

• Only say TARGET_LINK_LIBRARIES(hello SQLite::SQLite3)

• ⟶ All is fine

Demo Time

• Download into libhello/

  • 13-external-dependencies/libhello/greeter-alias-db.h

  • 13-external-dependencies/libhello/greeter-alias-db.cpp

• In libhello/greeter-alias-db.h, notice

  #include <sqlite3.h>
  

  • ⟶ found as /usr/include/sqlite3.h

  • Compiler looks there anyway

• Linked against SQLite library

  $ ldd bin/hello-third
         ...
         libsqlite3.so.0 => /lib64/libsqlite3.so.0 (0x00007f76ae011000)
         libz.so.1 => /lib64/libz.so.1 (0x00007f76adef7000)
         ...
  

  • Somebody must have told linker to look for sqlite3

  • That library in turn pulls in z