标准C++字符串string任意分割

实现字符串任意分割，如下程序，并有使用举例。
#include <vector>
#include <string>
#include <iostream>
#include <algorithm>
using namespace std;

typedef basic_string<char>::size_type S_T;  
static const S_T npos = -1; 

////trim指示是否保留空串，默认为保留。tok可以为任意多个字符
vector<string> tokenize(const string& src, string tok,            
                        bool trim=false, string null_subst="")  
{  
    if( src.empty() || tok.empty() ) 
        throw "tokenize: empty string/0";  
        
    vector<string> v;  
    S_T pre_index = 0, index = 0, len = 0;  
    while( (index = src.find_first_of(tok, pre_index)) !=npos )  
    {  
        if( (len = index-pre_index)!=0 )  
            v.push_back(src.substr(pre_index, len));  
        else if(trim==false)  
            v.push_back(null_subst);  
        pre_index = index+1;  
    }  
    string endstr = src.substr(pre_index);  
    if( trim==false ) v.push_back( endstr.empty()?null_subst:endstr );  
    else if( !endstr.empty() ) 
        v.push_back(endstr);  
    return v;  
} 
//delimit为一个字符，严格分割
vector<string> split(const string& src, string delimit, string null_subst="")  
{  
    if( src.empty() || delimit.empty() ) 
        throw "split:empty string/0";    
    vector<string> v;  
    S_T deli_len = delimit.size();  
    long index = npos, last_search_position = 0;  
    while( (index=src.find(delimit,     
        last_search_position))!=npos )  
    {  
        if(index==last_search_position)  
            v.push_back(null_subst);  
        else  
            v.push_back( src.substr(last_search_position, index-   
            last_search_position) );  
        last_search_position = index + deli_len;  
    }  
    string last_one = src.substr(last_search_position);  
    v.push_back( last_one.empty()? null_subst:last_one );  
    return v;  
}  

测试如下：
int main(int argc, char* argv[])
{
    string src = ",ab,cde;,,fg,," ;  
    string tok = ",;" ;   
    vector<string> v1 = tokenize(src, tok ,true);  
    vector<string> v2 = tokenize(src, tok ,false,     
        "<null>");    
    cout<<"-------------v1:"<<endl;  
    for(int i=0; i<v1.size();i++)  
    {  
        cout<<v1[i].c_str()<<endl;  
    }   
    cout<<"-------------v2:"<<endl;  
    for(int j=0; j<v2.size();j++)  
    {  
        cout<<v2[j].c_str()<<endl;  
    }  
    try{  
        
        string s = "1;2;3;4";  
        string del = ";";//"###";  
        vector<string> v3 = split(s, del, "<null>");  
        cout<<"-------------v3:"<<endl;  
        for(int k=0; k<v3.size();k++)  
        {  
            cout<<v3[k].c_str()<<endl;  
        }  
    }  
    catch (char *s) {  
        cout<<s<<endl;  
    }
    return 0;
}