find_first_of 源码剖析

原创

Limer123 2022-12-07 00:08:26 ©著作权

文章标签 find_first_of 源码 STL C++ #include 文章分类 虚拟化云计算

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一：用法解析

函数原型：

equality (1)
template <class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 find_first_of (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2);
predicate (2)
template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
ForwardIterator1 find_first_of (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred);

功能：

在区间[ first1 , last1 )里找到第一个可以与区间[ first2 , last2 )任意的某个值匹配的元素，返回其迭代器，找不到返回last1。

例子：

// find_first_of example
#include <iostream>     // std::cout
#include <algorithm>    // std::find_first_of
#include <vector>       // std::vector
#include <cctype>       // std::tolower

bool comp_case_insensitive (char c1, char c2) {
  return (std::tolower(c1)==std::tolower(c2));
}

int main () {
  int mychars[] = {'a','b','c','A','B','C'};
  std::vector<char> haystack (mychars,mychars+6);
  std::vector<char>::iterator it;

  int needle[] = {'A','B','C'};

  // using default comparison:
  it = find_first_of (haystack.begin(), haystack.end(), needle, needle+3);

  if (it!=haystack.end())
    std::cout << "The first match is: " << *it << '\n';

  // using predicate comparison:
  it = find_first_of (haystack.begin(), haystack.end(),
                      needle, needle+3, comp_case_insensitive);

  if (it!=haystack.end())
    std::cout << "The first match is: " << *it << '\n';

  return 0;
}

运行如下：

The first match is: A
The first match is: a

二：源码剖析

// TEMPLATE FUNCTION find_first_of WITH PRED
template<class _FwdIt1,
  class _FwdIt2,
  class _Pr> inline
  _FwdIt1 _Find_first_of(_FwdIt1 _First1, _FwdIt1 _Last1,
    _FwdIt2 _First2, _FwdIt2 _Last2, _Pr _Pred)
  { // look for one of [_First2, _Last2) satisfying _Pred with element
  for (; _First1 != _Last1; ++_First1)
    for (_FwdIt2 _Mid2 = _First2; _Mid2 != _Last2; ++_Mid2)
      if (_Pred(*_First1, *_Mid2))
        return (_First1);
  return (_First1);
  }

template<class _FwdIt1,
  class _FwdIt2,
  class _Pr> inline
  _FwdIt1 find_first_of(_FwdIt1 _First1, _FwdIt1 _Last1,
    _FwdIt2 _First2, _FwdIt2 _Last2, _Pr _Pred)
  { // look for one of [_First2, _Last2) satisfying _Pred with element
  _DEBUG_RANGE(_First1, _Last1);
  _DEBUG_RANGE(_First2, _Last2);
  _DEBUG_POINTER_IF(_First1 != _Last1 && _First2 != _Last2, _Pred);
  return (_Rechecked(_First1,
    _Find_first_of(_Unchecked(_First1), _Unchecked(_Last1),
      _Unchecked(_First2), _Unchecked(_Last2), _Pred)));
  }