C++ string中find() ，rfind() 等函數 用法總結及示例

string中 find()的應用  （rfind() 類似，只是從反向查找）
原型如下：
（1）size_t find (const string& str, size_t pos = 0) const;  //查找對象--string類對象
（2）size_t find (const char* s, size_t pos = 0) const; //查找對象--字符串
（3）size_t find (const char* s, size_t pos, size_t n) const;  //查找對象--字符串的前n個字符
（4）size_t find (char c, size_t pos = 0) const;  //查找對象--字符
結果：找到 -- 返回 第一個字符的索引
     沒找到--返回   string::npos
 
示例：
[cpp]
#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; 
} 

#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;
}

結果：
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
 
 
其他還有  find_first_of(), find_last_of(), find_first_not_of(), find_last_not_of()
作用是查找   字符串中 任一個字符 滿足的查找條件
string snake1("cobra");
int where = snake1.find_first_of("hark");
返回3  因為 "hark"中 各一個字符 在 snake1--cobra 中第一次出現的是  字符'r'（3為 cobra 中'r'的索引）
同理：
int where = snake1.find_last_of("hark");
返回4  因為 "hark"中 各一個字符 在 snake1--cobra 中最後一次出現的是  字符'a'（3為 cobra 中'r'的索引）
 
其他同理