How to print out debug info to terminal when running c++ with CMake?

I am reading a C++ project and want to print out the #ifdef _DEBUG message when running the program at a Linux terminal. For example:

#ifdef _DEBUG
            
            cout  << s1 << endl;
#endif

Currently, it doesn't print out the debug info above, but only prints out logger info as below:

logger_(MY_MODULE_LOG_ERROR, "config is null "); 

The project is made through cmake. It has a top level CMakeLists.txt file, in addition to each CZMakeLists.txt under src/ and its subdirectories. The content of the top-level CMakelists.txt is below:

cmake_minimum_required (VERSION 3.12)

project (TAGS_NEW )
set(CMAKE_VERBOSE_MAKEFILE true)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -fPIC -w")
# gdb debug : -g

add_compile_options(
    -Wall
    -Wextra
    -Wstrict-aliasing
    -Wno-unused-parameter
    -Wno-missing-field-initializers
    -Wchar-subscripts
    -Wpointer-arith
    -Wformat
    -Wformat-security
    -Werror=format-security
    -fstack-protector-all
    -fPIE
    -fpie
    -fPIC
    -fpic
    -pipe
    -fdata-sections
    -ffunction-sections
)

option(DEBUG_OUTPUT "option for debug out" OFF)
if (DEBUG_OUTPUT)
    add_definitions(-D_DEBUG)
endif()

# option(DEBUG_GDB "option for gdb debug" OFF)
# if (DEBUG_GDB)
#     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -ggdb")
# endif()

# set(CMAKE_BUILD_TYPE "Debug") 
option(CMAKE_BUILD_TYPE "option for gdb debug" DEBUG)
set(CMAKE_CXX_FLAGS_DEBUG "$ENV{CXXFLAGS} -O0 -Wall -g -ggdb")
set(CMAKE_CXX_FLAGS_RELEASE "$ENV{CXXFLAGS} -O3 -Wall")


option(COMPILE_DLL "option for generate dynamic library" OFF)

set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${TAGS_NEW_SOURCE_DIR}/output)

add_definitions(-D_Python_CALL  -D_ChaiScriptON)
include_directories(${TAGS_NEW_SOURCE_DIR}/third-party/include ${TAGS_MINING_NEW_SOURCE_DIR}/include )

# $(python -c "from distutils.sysconfig import get_python_inc; print(get_python_inc())")
find_package( PythonLibs 2.7 REQUIRED )
include_directories( ${PYTHON_INCLUDE_DIRS} )

link_directories(${TAGS_NEW_SOURCE_DIR}/third-party/lib)

add_subdirectory (src)

execute_process(COMMAND sh genGlobal.sh ${TAGS_NEW_SOURCE_DIR} WORKING_DIRECTORY  ${TAGS_NEW_SOURCE_DIR})

I tried to change the OFF to ON in the line below, but it doesn't help:

option(DEBUG_OUTPUT "option for debug out" OFF)

I am new to CMake. How to print out all the debug info?