C++中汉字字符串的截取

#include <iostream>
#include <string.h>
#include <stdio.h>
using namespace std;

#define MAX_SIZE 32

int chinese_split(std::string str,int index)  
{

    if(index > str.size())
        return 0;
    if((str[index]&0x80) == 0x80){
        if((str[index-1]& 0x80) == 0){
            return 1;
        }else{
            int n = 1;
            while(((str[index-n] &0x80) == 0x80 )&&((str[index-n] &0x40) == 0)){
                ++n;
            }
            return n;
        }
   }else{
    return 0;
   }
}
void my_strcpy(char *dst, const char *src , int index , int count = 10){
    if(strlen(src) > MAX_SIZE && index >4){
        int n = chinese_split(src,index);
        cout<<n<<endl;
        strncpy(dst,src,index-n);
    }else{
        strcpy(dst,src);
    }
}

 int main(){
    
    char a[] = "方案是ie以写文件的形式写下来，wifi热点模块在启动时会以读文件形式读取配置文件并且配置"; 
    char b[MAX_SIZE];
    
    cout<<"-----------"<<endl;
    for(int i=20;i<32; i++ ){
    memset(b,0,MAX_SIZE);
    my_strcpy(b,a,i);
    cout<< b<<endl;
    }
    return 0;
}