C++：string类的使用方法

size()、length()、capacity()： 

#include <iostream>
#include <string>

using namespace std;
int main()
{
    string s("test string");
    // size()和length()的作用一样，返回当前字符串s的长度
    cout << "size: " << str.size() << "\n";
    cout << "length: " << str.length() << "\n";
    // capacity() 当前分配给s的存储空间
    cout << "capacity: " << str.capacity() << "\n";  
    return 0；       
}

substr()

string substr(size_t pos = 0, size_t len = npos) const;

Returns a newly constructed string object with its value initialized to a copy of a substring of this object.

// string::substr
#include <iostream>
#include <string>

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

  std::string str2 = str.substr (3,5);     // "think"

  std::size_t pos = str.find("live");      // position of "live" in str

  std::string str3 = str.substr (pos);     // get from "live" to the end

  std::cout << str2 << ' ' << str3 << '\n';

  return 0;
}