程序代码：

#include <iostream>
#include <string>
using namespace std;
bool get_substr(const string & str,int pos/*截取位置，0开始*/,unsigned int length/*截取长度*/,char ** lpsubstr/*out*/)
{
    if(pos >= str.length())
        return false;
    if(pos + length >= str.length())
        length = str.length() - pos;
    *lpsubstr = new char[length+1];
    if(!*lpsubstr)
        return false;
    memset(*lpsubstr,0,length+1);
    memcpy(*lpsubstr,&str.c_str()[pos],length);
    return true;
}
int main()
{
    string str("1234567890");
    char * psubstr = NULL;
    if(get_substr(str,7,5,&psubstr) && psubstr)
    {
        cout <<psubstr<<endl;
        delete[] psubstr;
        psubstr = NULL;
    }
    system("pause");
    return 0;
}

程序代码：

// string::substr
#include <iostream>
#include <string>
using namespace std;

int main ()
{
  string str="We think in generalities, but we live in details.";
                             // quoting Alfred N. Whitehead
  string str2, str3;
  size_t pos;

  str2 = str.substr (12,12); // "generalities"

  pos = str.find("live");    // position of "live" in str
  str3 = str.substr (pos);   // get from "live" to the end

  cout << str2 << ' ' << str3 << endl;

  return 0;
}