The reason may be that Ceres did not specify the C + + version, but a-loam did. So make a-loam consistent with Ceres

Add the following code to cmakelists of a-loam

# Set the C++ version (must be >= C++14) when compiling Ceres.
#
# Reflect a user-specified (via -D) CMAKE_CXX_STANDARD if present, otherwise
# default to C++14.
set(DEFAULT_CXX_STANDARD ${CMAKE_CXX_STANDARD})
if (NOT DEFAULT_CXX_STANDARD)
  set(DEFAULT_CXX_STANDARD 14)
endif()
set(CMAKE_CXX_STANDARD ${DEFAULT_CXX_STANDARD} CACHE STRING
  "C++ standard (minimum 14)" FORCE)
# Restrict CMAKE_CXX_STANDARD to the valid versions permitted and ensure that
# if one was forced via -D that it is in the valid set.
set(ALLOWED_CXX_STANDARDS 14 17 20)
set_property(CACHE CMAKE_CXX_STANDARD PROPERTY STRINGS ${ALLOWED_CXX_STANDARDS})
list(FIND ALLOWED_CXX_STANDARDS ${CMAKE_CXX_STANDARD} POSITION)
if (POSITION LESS 0)
  message(FATAL_ERROR "Invalid CMAKE_CXX_STANDARD: ${CMAKE_CXX_STANDARD}. "
    "Must be one of: ${ALLOWED_CXX_STANDARDS}")
endif()
# Specify the standard as a hard requirement, otherwise CMAKE_CXX_STANDARD is
# interpreted as a suggestion that can decay *back* to lower versions.
set(CMAKE_CXX_STANDARD_REQUIRED ON CACHE BOOL "")
mark_as_advanced(CMAKE_CXX_STANDARD_REQUIRED)

There are other methods as follows, but I didn’t try

Modifying cmake: set the C + + standard:

set(CMAKE_CXX_FLAGS "-std=c++11")

Change to

set(CMAKE_CXX_STANDARD 11)