what's the properly cmakelists.txt for libpq library - postgresql

Question

I am trying to use libpq postgresql.
https://pgpedia.info/l/libpq.html
I copied the exact code.Trying to understand how to use cmake.
I am using Clion. (I guess the IDE doesn't matter.
The following part is CMakeLists.txt.
cmake_minimum_required(VERSION 3.23) project(test111 C)
set(CMAKE_C_STANDARD 99)
add_executable(test111 main.c)
find_package(PostgreSQL REQUIRED)
#target_include_directories(ecpg PUBLIC ${/usr/include/postgresql})
#target_link_libraries(ecpg PUBLIC ${PostgreSQL_LIBRARIES}
target_link_libraries(test111 PUBLIC ${/usr/lib/postgresql/15/lib})
#target_include_directories(MyTarget PRIVATE ${/usr/include/postgresql})
include_directories("/usr/include/postgresql")
using pg_config | rg PKG command return:
PKGINCLUDEDIR = /usr/include/postgresql
PKGLIBDIR = /usr/lib/postgresql/15/lib
Also mark this related to postgresql. I copy the exact code from https://pgpedia.info/l/libpq.html to c_libpqtest.c
gcc -o c_assert -I/usr/include/postgresql -L/usr/lib/postgresql/15/lib c_libpqtest.c
Still errors:
/usr/bin/ld: c_libpqtest.c:(.text+0x70): undefined reference to `PQstatus'
/usr/bin/ld: c_libpqtest.c:(.text+0x80): undefined reference to `PQerrorMessage'
/usr/bin/ld: c_libpqtest.c:(.text+0xbd): undefined reference to `PQexec'
/usr/bin/ld: c_libpqtest.c:(.text+0xd7): undefined reference to `PQgetvalue'
/usr/bin/ld: c_libpqtest.c:(.text+0xeb): undefined reference to `PQclear'
/usr/bin/ld: c_libpqtest.c:(.text+0xf7): undefined reference to `PQfinish'
collect2: error: ld returned 1 exit status
Update: The following compile ways will work. Reference: https://riptutorial.com/postgresql/example/8018/accessing-postgresql-with-the-c-api
gcc -Wall -o c_libpq -I/usr/include/postgresql -L/usr/lib/x86_64-linux-gnu c_libpqtest.c -lpq
gcc -Wall -o c_libpq -I "$(pg_config --includedir)" -L "$(pg_config --libdir)" c_libpqtest.c -lpq
gcc -o c_libpq -I/usr/include/postgresql -L/usr/lib/postgresql/14/lib c_libpqtest.c -lpq
Shared libpq library in /usr/lib/x86_64-linux-gnu
So overall I know how to use gcc command line solve this problem. I still don't know how to use cmake to solve the problem...

Answer 1

CMake provides a FindPostgreSQL.cmake module file, and it defines an imported target since 3.14: https://cmake.org/cmake/help/latest/module/FindPostgreSQL.html
So the most robust approach is:
cmake_minimum_required(VERSION 3.14)
project(myproject LANGUAGES C)
find_package(PostgreSQL REQUIRED)
add_executable(myapp main.c)
target_link_libraries(myapp PRIVATE PostgreSQL::PostgreSQL)