event.h: No such file or directory even when libevent-dev is installed

Question

I'm trying to compile a library that depends on libevent. The library is part of a bigger project using cmake build system that has a top-level CMakeLists.txt file.

The CMakelists.txt file within the library directory contains

target_include_directories(<library name> PRIVATE ${CMAKE_CURRENT_SOURCE_DIR} ${SOME_DEP_DIR}/include)
target_link_libraries(<library name> PUBLIC event)

libevent seems to be present on the system -

$ ldconfig -p | grep event
    libtevent.so.0 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libtevent.so.0
    libtevent-util.so.0 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libtevent-util.so.0
    libevent_pthreads-2.1.so.6 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libevent_pthreads-2.1.so.6
    libevent_openssl-2.1.so.6 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libevent_openssl-2.1.so.6
    libevent_extra-2.1.so.6 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libevent_extra-2.1.so.6
    libevent_core-2.1.so.6 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libevent_core-2.1.so.6
    libevent-2.1.so.6 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libevent-2.1.so.6

So is event.h

$ ls -l /usr/include/event.h 
-rw-r--r-- 1 root root 2744 Feb  5  2018 /usr/include/event.h

I also installed libevent-dev -

$ dpkg -l | grep libevent-dev
ii  libevent-dev                               2.1.8-stable-4build1                         amd64        Asynchronous event notification library (development files)

I'm not sure why when I run make library, I get the following error -

fatal error: event.h: No such file or directory
 #include <event.h>

Any suggestions would be helpful. Thanks!

Answer 1

You need to add path /usr/include to the list of include dirs.

target_include_directories(<library name> PRIVATE /usr/include ${CMAKE_CURRENT_SOURCE_DIR} ${SOME_DEP_DIR}/include)

UPDATE: A better approach is to use cmake's pkg-config module to find libraries that provide pkg-config's .pc file.

# Add pkg-config functionality
find_package(PkgConfig REQUIRED) 

# search for libevent.pc
pkg_search_module(EVENT REQUIRED libevent)

target_include_directories(<library name> PRIVATE ${EVENT_INCLUDE_DIRS} ${CMAKE_CURRENT_SOURCE_DIR} ${SOME_DEP_DIR}/include)
target_link_libraries(<library name> PUBLIC ${EVENT_LIBRARIES})

The libevent.pc contains all the necessary information that is required to successfully link against the library libevent.