C++string的操作

#include <iostream>
using namespace std;


int main()
{
    //initilization
    string            str("abc.ddd");
    const    string     cstr("fff.ccc");
    string substr1(str, 2); //c.ddd
    string substr2(str, 2, 3); //c.d
    string substr3("abcdefg", 2); //ab
    cout << "the value of substr1 is: " << substr1 << endl;
    cout << "the value of substr2 is: " << substr2 << endl;
    cout << "the value of substr3 is: " << substr3 << endl;

    //compare
    if(str > cstr)
        cout << "abc.ddd is larger than fff.ccc." << endl;
    else
        cout << "abc.ddd is less than fff.ccc." << endl;
    if(str.compare(cstr) > 0)
        cout << "abc.ddd is larger than fff.ccc." << endl;
    else
        cout << "abc.ddd is less than fff.ccc." << endl;

    //assign
    str = "sadfasdf";
    str.assign("a",5); //a,\0,\0,\0,\0
    str.assign(5,'a'); //a, a, a, a, a
    cout << "the value of str is: " << str << endl; //aaaaa

    //append
    str.append("bcd");
    cout << "the value of s after append is: " << str << endl; //aaaaabcd
    
    //insert
    //s.insert(1, 'd'); NOK!
    str.insert(1, "ddd"); //adddaaaabcd
    cout << "the value of s after append is: " << str << endl;
    
    //find
    string::size_type idx = str.find(".");
    cout << "the index of . is: " << idx << endl; //3

    //substring
    string basestr = str.substr(0, idx); //abc
    string extestr = str.substr(idx + 1, string::npos); //ddd
    cout << "the substr of str.substr(0, idx) is: " << basestr << endl;
    cout << "the substr of str.substr(idx, string::npos) is: " << extestr << endl;

    //compare
    if(extestr == "ddd")
        cout << "ddd file is found!" << endl;
    else
        cout << "ddd file is not found!" << endl;
    
    //replace
    string tmpname(str.replace(idx + 1, string::npos, "xxx")); //abc.xxx
    cout << "the string after replace extention is: " << tmpname << endl;

    //erase
    str = "internal";
    str.replace(0,2,"ex"); //external
    str.erase(5);
    str.erase(2,2);
    cout << "the string after erase is: " << str << endl;

    //clear
    str.clear();
    cout << "the string after clear is: " << str << endl;
    if(str.empty())
        cout << "the string is empty." << endl;
    else
        cout << "the string is not empty." << endl;
    if(str.begin() == str.end())
        cout << "equal." << endl;
    else
        cout << "unequal" << endl;

    //reverse
    str = "abcd";
    reverse(str.begin(), str.end());
    cout << "the string after reverse is: " << str << endl;
    str.assign(str.rbegin(), str.rend());
    cout << "the string after reverse is: " << str << endl;

    //data
    const char* pa = str.data();

    //size(), length()
    cout << "the size of str is: " << str.size() << endl;
    cout << "the size of str is: " << str.length() << endl;

    //[], at()
    char& r = str[2];
    char* p = &str[3];
    cout << "the 3rd char of str is: " << r << endl;
    cout << "the 4rd char of str is: " << *p << endl;
    str = "new value";
    //reference is invalid after str is re-assigned
    r = 'X';
    cout << "The value of str is: " << str << endl;

    //advanced find    
    //Input: I was a deer
    //Output: reed a saw I
    const string delims(" \t,.;");
    string line;
    cout << "Please input a sentence: " << endl;
    getline(cin, line,'\n');
    cout << "The input sentence is: " << line << endl;
    //while find a word
    string::size_type begIdx, endIdx;
    begIdx = line.find_first_not_of(delims);
    while(begIdx != string::npos){
        endIdx = line.find_first_of(delims, begIdx); 
        if(endIdx == string::npos);
            //endIdx = line.length();
        for(int i = endIdx - 1; i >= static_cast<int>(begIdx); --i)
            cout << line[i];
        cout << ' '; 
        begIdx = line.find_first_not_of(delims, endIdx);

    }
    cout << endl;

}