std::find

template <class InputIterator, class T>
   InputIterator find (InputIterator first, InputIterator last, const T& val);

Returns an iterator to the first element in the range [first,last) that compares equal to val. If no such element is found, the function returns last.

返回范围内与val相等的第一个元素的迭代器，如果没有这样的元素，那么将返回last.

例子：

#include <iostream>
#include <algorithm>
#include <vector>
#include <array>
using namespace std;

void find2(){
    vector<int> vi{1,5,7,8,9,9,8,5,9};
    cout<<"vi=";
    for(int &i:vi)
        cout<<i<<" ";
    cout<<endl;

    auto it=find(vi.begin(),vi.end(),8);
    cout<<"auto it=find(vi.begin(),vi.end(),8);"<<endl;
    cout<<"(it-1)="<<*(it-1)<<endl;
    cout<<"it="<<*it<<endl;
    cout<<"(it+1)="<<*(it+1)<<endl;

    auto it2=find(vi.begin(),vi.end(),18);
    cout<<"auto it2=find(vi.begin(),vi.end(),18);"<<endl;
    cout<<"(it2-1)="<<*(it2-1)<<endl;
    cout<<"it2="<<*it2<<endl;
    cout<<"(it2+1)="<<*(it2+1)<<endl;
    if(it2==vi.end())
        cout<<"it2==vi.end()"<<endl;


}

运行截图：

The function uses operator== to compare the individual elements to val.

使用operator==来比较元素与val是否相等。

The behavior of this function template is equivalent to:

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template<class InputIterator, class T>
  InputIterator find (InputIterator first, InputIterator last, const T& val)
{
  while (first!=last) {
    if (*first==val) return first;
    ++first;
  }
  return last;
}

Parameters

first, last

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

val

Value to search for in the range.
T shall be a type supporting comparisons with the elements pointed by InputIterator using operator== (with the elements as left-hand side operands, and val as right-hand side).

比较的值。

Return value

An iterator to the first element in the range that compares equal to val.
If no elements match, the function returns last.

返回范围内与val相等的第一个元素的迭代器，如果没有这样的元素，那么将返回last.

Example

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

int main () {
  // using std::find with array and pointer:
  int myints[] = { 10, 20, 30, 40 };
  int * p;

  p = std::find (myints, myints+4, 30);
  if (p != myints+4)
    std::cout << "Element found in myints: " << *p << '\n';
  else
    std::cout << "Element not found in myints\n";

  // using std::find with vector and iterator:
  std::vector<int> myvector (myints,myints+4);
  std::vector<int>::iterator it;

  it = find (myvector.begin(), myvector.end(), 30);
  if (it != myvector.end())
    std::cout << "Element found in myvector: " << *it << '\n';
  else
    std::cout << "Element not found in myints\n";

  return 0;
}

Output:

Element found in myints: 30
Element found in myvector: 30

Complexity

Up to linear in the distance between first and last: Compares elements 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 an element comparison or an operation on an iterator throws.
Note that invalid arguments 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

2014-9-11

于GDUT

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