Multiples CMake in a project - c++

Question

I'm developing a C++ application that use a library that i develop before. I don`t want link the binary to my new project because who use another plataform need rebuild then. So, i whant attach the cmake file from this another project to this new one and when i build then, build the library too. Someone know how i do this? Thanks Alot.
String Library: https://github.com/TigreFramework/String
My new CMake file:
cmake_minimum_required(VERSION 3.4)
project(DataBase)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
set(SOURCE_FILES main.cpp DataBase.cpp DataBase.h String.h libString.a)
add_executable(DataBase ${SOURCE_FILES})
EDIT 01:
Now i can compile with this CMake:
cmake_minimum_required(VERSION 3.4)
project(String)
include_directories(./include/cryptopp563/)
#link_directories(./include/cryptopp563/)
add_subdirectory(./include/cryptopp563/)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
find_library(cryptopp include/cryptopp563/)
set(SOURCE_FILES main.cpp String.cpp String.h RsaString.cpp RsaString.h)
add_library(RsaString STATIC RsaString.cpp)
add_library(String STATIC String.cpp)
#add_executable(Teste ${SOURCE_FILES})
But, if i use de add_executable i receive this error:
[ 1%] Built target String
[ 2%] Built target RsaString
[ 2%] Linking CXX executable Teste
[ 97%] Built target cryptopp
Undefined symbols for architecture x86_64:
"CryptoPP::RandomPool::IncorporateEntropy(unsigned char const*, unsigned long)", referenced from:
vtable for CryptoPP::AutoSeededRandomPool in String.cpp.o
"CryptoPP::RandomPool::GenerateIntoBufferedTransformation(CryptoPP::BufferedTransformation&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, unsigned long long)", referenced from:
vtable for CryptoPP::AutoSeededRandomPool in String.cpp.o
"CryptoPP::RandomPool::RandomPool()", referenced from:
CryptoPP::AutoSeededRandomPool::AutoSeededRandomPool(bool, unsigned int) in String.cpp.o
.............. MORE LINES HIDEM HERE .................
"non-virtual thunk to CryptoPP::BufferedTransformation::GetWaitObjects(CryptoPP::WaitObjectContainer&, CryptoPP::CallStack const&)", referenced from:
vtable for CryptoPP::SourceTemplate<CryptoPP::FileStore> in RsaString.cpp.o
vtable for CryptoPP::FileSource in RsaString.cpp.o
vtable for CryptoPP::AutoSignaling<CryptoPP::InputRejecting<CryptoPP::BufferedTransformation> > in RsaString.cpp.o
vtable for CryptoPP::InputRejecting<CryptoPP::BufferedTransformation> in RsaString.cpp.o
vtable for CryptoPP::InputRejecting<CryptoPP::Filter> in RsaString.cpp.o
vtable for CryptoPP::Sink in RsaString.cpp.o
vtable for CryptoPP::PK_DecryptorFilter in RsaString.cpp.o
...
"non-virtual thunk to CryptoPP::BufferedTransformation::GetMaxWaitObjectCount() const", referenced from:
vtable for CryptoPP::SourceTemplate<CryptoPP::FileStore> in RsaString.cpp.o
vtable for CryptoPP::FileSource in RsaString.cpp.o
vtable for CryptoPP::AutoSignaling<CryptoPP::InputRejecting<CryptoPP::BufferedTransformation> > in RsaString.cpp.o
vtable for CryptoPP::InputRejecting<CryptoPP::BufferedTransformation> in RsaString.cpp.o
vtable for CryptoPP::InputRejecting<CryptoPP::Filter> in RsaString.cpp.o
vtable for CryptoPP::Sink in RsaString.cpp.o
vtable for CryptoPP::PK_DecryptorFilter in RsaString.cpp.o
...
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
CMakeFiles/Teste.dir/build.make:146: recipe for target 'Teste' failed
gmake[2]: *** [Teste] Error 1
CMakeFiles/Makefile2:141: recipe for target 'CMakeFiles/Teste.dir/all' failed
gmake[1]: *** [CMakeFiles/Teste.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
gmake: *** [all] Error 2

Answer 1

You can use add_subdirectory https://cmake.org/cmake/help/v3.0/command/add_subdirectory.html
or simple include
https://cmake.org/cmake/help/v3.0/command/include.html
also there is feature of cmake called external project,
which allow you to build project with any build system
https://cmake.org/cmake/help/v3.0/module/ExternalProject.html