Create a Shared library and use it in another project - c++11

Question

I have a c++ project with following structure:
.
├── include
│ ├── common.h
│ ├── os.h
│ ├── helper.h
│
├── lib
| ├── libcrypto.so
│ ├── libssl.so
| ├── ...
|
└── src
├── common.c
├── helper.c
Now I want to make a shared or any kind of library of this whole project so that I can include helper.h header in some other c++ project totally independent of this one and call some function declared in this header file.
I tried making a shared library with the following CMakeLists file:
cmake_minimum_required(VERSION 3.0)
project(helperlib)
link_directories(lib)
file(GLOB SOURCES src/*.c)
include_directories(include)
add_library(${PROJECT_NAME} SHARED ${SOURCES})
install(TARGETS ${PROJECT_NAME} DESTINATION lib/${PROJECT_NAME})
file(GLOB HEADERS include/*.h)
install(FILES ${HEADERS} DESTINATION include/${PROJECT_NAME})
But when I use the libhelperlib.so file generated by cmake in another project and use #include "helper.h", it gives me error.
Can anyone suggest how to do this.
Thanks!
EDIT:
This is the structure of the other project:
.
├── include
│ ├── constants.h
│ ├── datetime.h
│ ├──
│
├── lib
| ├── libhelperlib.so
│ ├── libboost_system.so
| ├── liboost_system.a
|
└── src
├── constants.c
├── datetime.c
├── main.c
And CMakeLists.txt that I'm using for it is:
cmake_minimum_required(VERSION 3.0)
project(testProj)
include_directories(include)
link_directories(lib)
file(GLOB SOURCES src/*.c)
file(GLOB HEADERS include/*.h)
add_executable(testProj ${SOURCES} ${HEADERS})
target_link_libraries(testProj crypto helperlib boost_system)
And when I'm using #include "helper.h" in main .c it gives following error:
fatal error: helper.h: No such file or directory