C++ String trim function

#include <iostream>
#include <string>
 
using namespace std;
 
void __trim(std::string &str,bool trim_left,bool trim_right)
{
    std::string::size_type begin=0;
    std::string::size_type end=str.size()-1;
    while(left && begin<=end && (str[begin]<=0x20 || str[begin]==0x7f))
        ++begin;
    while(right && end>begin && (str[end]<=0x20 || str[end]==0x7f))
      --end;
    str = str.substr(begin, end - begin + 1);
}
void trim(std::string &str)  { __trim(str,1,1); }
void ltrim(std::string &str) { __trim(str,1,0); }
void rtrim(std::string &str) { __trim(str,0,1); }
 
int main(int argc, char **argv)
{
    string v1 = "   \n\r\tALPHA\r\t\n   ";
    trim(v1);
    string v2 = "   \n\r\tALPHA\r\t\n   ";
    ltrim(v2);
    string v3 = "   \n\r\tALPHA\r\t\n   ";
    rtrim(v3);
    cout << "|" << v1 << "|" << endl;
    cout << "|" << v2 << "|" << endl;
    cout << "|" << v3 << "|" << endl;
    return 0;
}