原文地址：http://www.cplusplus.com/reference/algorithm/find_if/

std::find_if

template <class InputIterator, class UnaryPredicate>
   InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred);

Returns an iterator to the first element in the range [first,last) for which pred returns true. If no such element is found, the function returns last.
返回范围内第一个符合要求的元素的迭代器，如果没有，则返回last.

#include <iostream>
#include <vector>
#include <array>
#include <algorithm>
using namespace std;
void findif()
{
    vector<int> v1{1,2,3,4,5,6,3,4,9,8};
    array<double,2> ai{77,88};

    cout<<"v1=";
    for(int &i:v1)
        cout<<i<<"  ";
    cout<<endl;


    cout<<endl<<"ai=";
    for(double &i:ai)
        cout<<i<<"  ";

    cout<<endl<<"auto it=find_if(v1.begin(),v1.end(),[](int i){return i%5==0;});"<<endl;
    auto it=find_if(v1.begin(),v1.end(),[](int i){return i%5==0;});
    cout<<"*(it-1)="<<*(it-1)<<endl;
    cout<<"*it="<<*it<<endl;
    cout<<"*(it+1)="<<*(it+1)<<endl;


    cout<<endl<<"auto it2=find_first_of(v1.begin(),v1.end(),ai.begin(),ai.end());"<<endl;
    auto it2=find_if(ai.begin(),ai.end(),[](int i){return i%100==0;});
    cout<<"*(it2-1)="<<*(it2-1)<<endl;
    cout<<"*it2="<<*it2<<endl;
    cout<<"*(it2+1)="<<*(it2+1)<<endl;

}

运行截图：

The behavior of this function template is equivalent to:

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template<class InputIterator, class UnaryPredicate>
  InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred)
{
  while (first!=last) {
    if (pred(*first)) return first;
    ++first;
  }
  return last;
}

Parameters

first, last

Input iterators to the initial and final positions in a sequence. The range used
is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
匹配的范围。

pred

Unary function that accepts an element in the range as argument and returns a value convertible to bool. The value returned indicates whether the element is considered a match in the context
of this function.
The function shall not modify its argument.
This can either be a function pointer or a function object.

一元函数。（接受一个参数的一元函数，返回一个bool值）

Return value

An iterator to the first element in the range for which pred does not return false.
If pred is false for all elements, the function returns last.

返回范围内第一个符合要求的元素的迭代器，如果没有，则返回last.

Example

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// find_if example
#include <iostream>     // std::cout
#include <algorithm>    // std::find_if
#include <vector>       // std::vector

bool IsOdd (int i) {
  return ((i%2)==1);
}

int main () {
  std::vector<int> myvector;

  myvector.push_back(10);
  myvector.push_back(25);
  myvector.push_back(40);
  myvector.push_back(55);

  std::vector<int>::iterator it = std::find_if (myvector.begin(), myvector.end(), IsOdd);
  std::cout << "The first odd value is " << *it << '\n';

  return 0;
}

Output:

The first odd value is 25

Complexity

Up to linear in the distance between first and last: Calls pred for each element until
a match is found.

Data races

Some (or all) of the objects in the range [first,last) are accessed (once at most).

Exceptions

Throws if either pred or an operation on an iterator throws.
Note that invalid parameters cause undefined behavior.

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转载请注明出处：http://blog.csdn.net/qq844352155

author:天下无双

Email:coderguang@gmail.com

2014-9-12

于GDUT

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