When working in a C or C++ project using CMake as a build process manager, it is almost a given that a set of external libraries will be used to aid the development of complex systems reliant on variety of functions such as low-level system access, database connectivity, etc.

To be able to use external libraries in a standard Makefile, it is usually done by setting a set of flags, canonically known as LDFLAGS. Here is an example of a Makefile that links PostgreSQL driver libraries to the project as well as the C++ Standard Library (which does not come pre-packaged in the case of gcc compiler).

Example Makefile

CC=gcc
LDFLAGS=-lstdc++ -lpqxx -lpq

all: main

main:
	$(CC) $(LDFLAGS) main.cpp -o main

In CMake, to make the same configuration viable, here is a way that CMakeLists.txt can be configured to produce the same result:

Example CMakeLists.txt

cmake_minimum_required(VERSION 3.13)
project(cpp_example)

set(CMAKE_CXX_STANDARD 14)
set(CMAKE_C_COMPILER gcc)
set(CMAKE_CXX_COMPILER gcc)

# Link stdc++, libpqxx, and libpq
set(CMAKE_EXE_LINKER_FLAGS "-lstdc++ -lpqxx -lpq")

add_executable(cpp_example main.cpp)