C++/C--string中的find()、find_first_of()、find_first_not_of()【轉載】

1 find()函數

功能：可以在指定字符串中查找完全匹配子串的位置；

示例：

// string::find
#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);//尋找的字符串來自於“needles are small”中的前6個字符
  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");
  std::cout << str << '\n';

  return 0;
}

運行結果：

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.

2 find_fisrt_of()函數

功能：查找在字符串中第一個與子串中的某個字符匹配的字符，返回它的位置，如果沒找到就返回string::npos；

示例：

// string::find_first_of
#include <iostream>       // std::cout
#include <string>         // std::string
#include <cstddef>        // std::size_t

int main ()
{
  std::string str ("Please, replace the vowels in this sentence by asterisks.");//asterisks，即'*'號
  std::size_t found = str.find_first_of("aeiou");
  while (found!=std::string::npos)
  {
    str[found]='*';
    found=str.find_first_of("aeiou",found+1);
  }

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

  return 0;
}

運行結果：

Pl**s*, r*pl*c* th* v*w*ls *n th*s s*nt*nc* by *st*r*sks.

3 find_fisrt_not_of()函數

功能：返回在字符串中首次出現的不匹配子串任何字符的首字符索引, 從index開始搜索, 如果全部匹配則返回string::npos；

示例：

// string::find_first_not_of
#include <iostream>       // std::cout
#include <string>         // std::string
#include <cstddef>        // std::size_t

int main ()
{
  std::string str ("look for non-alphabetic characters...");

  std::size_t found = str.find_first_not_of("abcdefghijklmnopqrstuvwxyz ");

  if (found!=std::string::npos)
  {
    std::cout << "The first non-alphabetic character is " << str[found];
    std::cout << " at position " << found << '\n';
  }

  return 0;
}

運行結果：

The first non-alphabetic character is - at position 12

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以上內容來自：

1. Scott_dingg_string 中的 find()、 find_first_of()、find_first_not_of()
2. www.cplusplus.com