c++ string rfind find函数

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1）size_t find (const string& str, size_t pos = 0) const; //查找对象–string类对象
（2）size_t find (const char s, size_t pos = 0) const; //查找对象–字符串

（3）size_t find (const char s, size_t pos, size_t n) const; //查找对象–字符串的前n个字符
（4）size_t find (char c, size_t pos = 0) const; //查找对象–字符
结果：找到 – 返回 第一个字符的索引

string::rfind(string, pos) 是从pos开始由右往左找，返回最后一次出现string的位置。

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#include <iostream>       // std::cout
#include <string>         // std::string
 
int main ()
{
  std::string str ("There are two needles in this haystack with needles.");
  std::string str2 ("needle");
 
  // different member versions of find in the same order as above:
  std::size_t found = str.find(str2);
  if (found!=std::string::npos)
    std::cout << "first 'needle' found at: " << found << '\n';
 
  found=str.find("needles are small",found+1,6);
  if (found!=std::string::npos)
    std::cout << "second 'needle' found at: " << found << '\n';
 
  found=str.find("haystack");
  if (found!=std::string::npos)
    std::cout << "'haystack' also found at: " << found << '\n';
 
  found=str.find('.');
  if (found!=std::string::npos)
    std::cout << "Period found at: " << found << '\n';
 
  // let's replace the first needle:
  str.replace(str.find(str2),str2.length(),"preposition");  //replace 用法
  std::cout << str << '\n';
 
  return 0;


结果：
first 'needle' found at: 14
second 'needle' found at: 44
'haystack' also found at: 30
Period found at: 51
There are two prepositions in this haystack with needles
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// string::rfind
#include <iostream>
#include <string>
#include <cstddef>
using namespace std;
int main ()
{
  std::string str ("The sixth sick sheik's sixth sheep's sick.");
  std::string key ("sixth");
//从起始位置 从右往左找 
  std::size_t found = str.rfind(key,3);
  if (found!=std::string::npos)
    str.replace (found,key.length(),"seventh");

  std::cout << str << '\n';

  return 0;
}