c++ pass function as argument

//util.cpp
#include "model/util.h"

void util::invoke_func_args(const util &ul, const int &len)
{
    util ulcopy=ul;
    pass_func_args(ulcopy,len,&get_str_uuid2);
    pass_func_args(ulcopy,len,&get_char_uuid);
}

void util::pass_func_args(util&ul,const int&len,void(*func)(util&,const int&))
{
    std::chrono::time_point<std::chrono::high_resolution_clock> start_time,end_time;
    start_time=std::chrono::high_resolution_clock::now();
    func(ul,len);
    end_time=std::chrono::high_resolution_clock::now();
    std::cout<<"Time cost "<<
    std::chrono::duration_cast<std::chrono::milliseconds>(end_time-start_time).count()<<" milliseconds!"<<std::endl<<std::endl;
}

void util::get_str_uuid2(util &ul,const int& len)
{
    for(int i=0;i<len;i++)
    {
        ul.get_str_uuid();
    }
}

void util::get_char_uuid(util &ul,const int& len)
{ 
    for(int i=0;i<len;i++)
    {
        ul.get_uuid();
    }
}



std::string util::get_str_uuid()
{
    uuid_t new_uuid;
    uuid_generate(new_uuid);
    uuid_unparse(new_uuid,uuid_value);
    return std::string(uuid_value);
}

char *util::get_uuid()
{
    uuid_t new_uuid;
    uuid_generate(new_uuid);
    uuid_unparse(new_uuid, uuid_value);
    return uuid_value;
}


//main.cpp
#include <unistd.h>
#include <stdio.h>
#include <time.h>
#include "model/util.h"

void invoke_func_args_demo(const int &len)
{ 
    util ul;
    ul.invoke_func_args(ul,len);
}

int main(int argc, char **argv)
{
    invoke_func_args_demo(atoi(argv[1]));     
}

g++ -g -std=c++2a -I. *.cpp ./model/*.cpp -o h1 -luuid -lpthread

//std::function<void(util &,const int &)>func
//func(ul,len)

void util::stdfunction_invoke_func(util &ul,const int &len)
{ 

    stdfunction_pass_func(ul,len,&get_str_uuid2);
    stdfunction_pass_func(ul,len,&get_char_uuid);
}

void util::stdfunction_pass_func(util &ul,const int &len,std::function<void(util &,const int &)>func)
{
    std::chrono::time_point<std::chrono::high_resolution_clock> start_time,end_time;
    start_time=std::chrono::high_resolution_clock::now();
    func(ul,len); 
    end_time=std::chrono::high_resolution_clock::now();
    std::uint64_t mills_count=std::chrono::duration_cast<std::chrono::milliseconds>(end_time-start_time).count();
    std::cout<<"Len="<<",Total Time cost "<<mills_count
    <<" milliseconds!"<<",Per Million Time cost "<<mills_count/(len/1000000)<<" milliseconds!"<<std::endl<<std::endl;
}

void util::stdfunction_invoke_func(util &ul,const int &len)
{     
    stdfunction_pass_func(ul,len,&get_char_uuid);
}

void util::stdfunction_pass_func(util &ul,const int &len,std::function<void(util &,const int &)>func)
{
    std::chrono::time_point<std::chrono::high_resolution_clock> start_time,end_time;
    start_time=std::chrono::high_resolution_clock::now();
    func(ul,len); 
    end_time=std::chrono::high_resolution_clock::now();
    std::uint64_t mills_count=std::chrono::duration_cast<std::chrono::milliseconds>(end_time-start_time).count();
    std::cout<<"Len="<<len<<",Total Time cost "<<mills_count
    <<" milliseconds!"<<",Per Million Time cost "<<mills_count/(len/1000000)<<" milliseconds!"<<std::endl<<std::endl;
}