从C语言到C++_11(string类的常用函数)力扣58和415（中）

void test_string3()
{
  string s1("hello world");
  s1[0] = 'x';
  //s1[20];  内部会检查越界
  cout << s1 << endl;
 
  for (size_t i = 0; i < s1.size(); ++i)// 普通遍历string，每个字符+1
  {
    s1[i]++;
  }
  cout << s1 << endl;
 
  string::iterator it = s1.begin();// 迭代器遍历string，每个字符+1
  while (it != s1.end())
  {
    (*it)++;
    it++;
  }
  cout << s1 << endl;
 
  for (auto& e : s1)// 范围for遍历string，每个字符-1
  {
    e--;
  }
  cout << s1 << endl;
 
  string::reverse_iterator rit = s1.rbegin();// 迭代器逆置遍历string，每个字符-1
  while (rit != s1.rend())
  {
    cout << *rit;
    (*rit)--;
    ++rit;// 注意这里也是++
  }
  cout << endl;
  
  *(s1.begin()) = 'h';// 把第一个字母改成h -> s1[0] = 'h';
  cout << s1 << endl;
}

void test_string4()
{
  string s("hello");
  s.push_back('-');
  s.push_back('-');
  s.append("world");
  cout << s << endl;
 
  string str("abcdefg");
  s += '@';
  s += str;
  s += "!!!";
  cout << s << endl;
 
  s.append(++str.begin(), --str.end());
  cout << s << endl;
 
  string copy(s.begin() + 3, s.end() - 3);
  cout << copy << endl;
 
  int ival = 2023;
  double dval = 3.14;
  cout << to_string(ival) << endl;
  cout << to_string(dval) << endl;
 
  string istr = "9999";
  string dstr = "9999.99";
  cout << stoi(istr) << endl;
  cout << stod(dstr) << endl;
}

void DealUrl(const string& url)
{
  // 取出协议
  size_t pos1 = url.find("://");
  if (pos1 == string::npos)
  {
    cout << "非法url" << endl;
    return;
  }
  string protocol = url.substr(0, pos1);
  cout << protocol << endl;
 
  // 取出域名
  size_t pos2 = url.find('/', pos1 + 3);// 冒号位置+3开始往后找
  if (pos2 == string::npos)
  {
    cout << "非法url" << endl;
    return;
  }
  string domain = url.substr(pos1 + 3, pos2 - pos1 - 3);
  cout << domain << endl;
 
  // 取出路径
  string uri = url.substr(pos2 + 1);
  cout << uri << endl << endl;
}
 
void test_string5()
{
  string filename("test.cpp.tar.zip");// 取后缀
  size_t pos = filename.rfind('.');// 反向找
  if (pos != string::npos)
  {
    //string suff = filename.substr(pos, filename.size() - pos);
    string suff = filename.substr(pos);//不用像上一行算长度，直接让默认值取到最后
 
    cout << suff << endl;
  }
 
  string url1 = "https://cplusplus.com/reference/string/string/";// 对一个网址进行操作，可以多放几个试试
  DealUrl(url1);
}

int main()
{
  string a = "hello world";
  string b = a;
  if (a.c_str() == b.c_str())
  {
    cout << "true" << endl;
  }
  else cout << "false" << endl;
  string c = b;
  c = "";
  if (a.c_str() == b.c_str())
  {
    cout << "true" << endl;
  }
  else cout << "false" << endl;
  a = "";
  if (a.c_str() == b.c_str())
  {
    cout << "true" << endl;
  }
  else cout << "false" << endl;
  return 0;
}

int main()
{
  string str("hello world");
  str.reserve(111);
  str.resize(5);
  str.reserve(50);
  cout << str.size() << " " << str.capacity() << endl;
  return 0;
}

int main()
{
  string strText = "How are you?";
  string strSeparator = " ";
  string strResult;
  int size_pos = 0;
  int size_prev_pos = 0;
  while ((size_pos = strText.find_first_of(strSeparator, size_pos)) != string::npos)
  {
    strResult = strText.substr(size_prev_pos, size_pos - size_prev_pos);
    cout << strResult << " ";
    size_prev_pos = ++size_pos;
  }
  if (size_prev_pos != strText.size())
  {
    strResult = strText.substr(size_prev_pos, size_pos - size_prev_pos);
    cout << strResult << " ";
  }
  cout << endl;
  return 0;
}