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

std::fill_n

template <class OutputIterator, class Size, class T>
  OutputIterator fill_n (OutputIterator first, Size n, const T& val);

Assigns val to the first n elements of the sequence pointed by first.
从first开始，将之后n个元素的值变为val.
例子：

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

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

    auto it=fill_n(vi.begin()+3,4,1000);
    cout<<"after     fill_n(vi.begin()+3,4,1000),\nvi=";
    for(int &i:vi)
        cout<<i<<" ";
    cout<<endl;
    cout<<"it="<<*it<<endl;

}

运行截图：

The behavior of this function template is equivalent to:

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template <class OutputIterator, class Size, class T>
  OutputIterator fill_n (OutputIterator first, Size n, const T& val)
{
  while (n>0) {
    *first = val;
    ++first; --n;
  }
  return first;     // since C++11
}

Parameters

first

Output iterators to the initial position in a sequence of at least n elements
that support being assigned a value of type T.
开始的位置。

n

Number of elements to fill.

• C++98
• C++11

If negative, the function does nothing.

Size shall be (convertible to) an integral type.
要被调整的元素个数。（如果是负数，不会做任何事情）

val

Value to be used to fill the range.
要填充的值。

Return value

返回值为一个指向最后一个被填充的元素的下一个元素的位置。

Example

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

int main () {
  std::vector<int> myvector (8,10);        // myvector: 10 10 10 10 10 10 10 10

  std::fill_n (myvector.begin(),4,20);     // myvector: 20 20 20 20 10 10 10 10
  std::fill_n (myvector.begin()+3,3,33);   // myvector: 20 20 20 33 33 33 10 10

  std::cout << "myvector contains:";
  for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
    std::cout << ' ' << *it;
  std::cout << '\n';

  return 0;
}

Output:

myvector contains: 20 20 20 33 33 33 10 10

Complexity

Linear in n: Assigns a value to each element.

Data races

The n first objects at the range pointed by first are modified (each object is modified exactly once).

Exceptions

Throws if either an element assignment 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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