boost::algorithm::split_regex doesn't work with boost::u32regex.

使用 CMakeLists.txt 配置复现 src.cpp 中的行为，并在 UTF-8 示例上比较 split_regex 与 u32regex_replace。从 boost::algorithm split_regex 入口点及其正则表达式处理开始；当示例被拆分为预期的 token，且有回归测试覆盖该行为时，即视为完成。

I want to split a UTF-8 string into tokens. However it looks like that split_regex() failed and just return original string. I also tried u32regex_replace() and it indeed replaced successfully.

src.cpp:

// CutWord.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
#include<vector>
#include<string>

#include <boost/algorithm/string.hpp>
#include<boost/algorithm/string/regex.hpp>
#include <boost/regex/icu.hpp> 
#include<regex>

using namespace std;

int main()
{
	string str="数学。数学。数学。";
	
	//Split
	vector<string> vs;
        //regexU3 stores expression.
	boost::u32regex regexU32= boost::make_u32regex("。");
	boost::split_regex(vs, str,regexU32);
	cout<<vs.size()<<endl; //only return 1.
	
	//Check if u32regex_replace works.
	string nsub=".";
	string nstr=u32regex_replace(str, regexU32, nsub);
	cout<<nstr<<endl;
};

CMakeLists.txt:

cmake_minimum_required(VERSION 3.10)
project(main)
set(CMAKE_C_COMPILER /usr/bin/gcc CACHE PATH "" FORCE)
set(CMAKE_CXX_COMPILER /usr/bin/g++ CACHE PATH "" FORCE)

include_directories("/usr/local/include")
include_directories("./include")

add_executable(mp src.cpp)

#ICU
find_package(ICU COMPONENTS i18n  io dt in uc)
target_link_libraries(mp ${ICU_LIBRARIES})

#boost
find_package( Boost COMPONENTS regex)
include_directories(${Boost_INCLUDE_DIR})
link_directories(${Boost_LIBRARY_DIR})
target_link_libraries( mp ${Boost_LIBRARIES} )

target_compile_features(mp PUBLIC cxx_std_20)
add_custom_command(TARGET mp POST_BUILD
	COMMAND echo "----------------------------------------------"
	COMMAND ./mp
	COMMAND echo "----------------------------------------------")