C++语法基础--泛型算法（generic algorithm)--写入容器元素的算法fill(),fill_n,replace()

刺骨的言语ヽ痛彻心扉 2022-01-11 23:37 201阅读 0赞

**\*fill  
Assigns val to all the elements in the range \[first,last)  
原型：  
template <class ForwardIterator, class T>  
void fill (ForwardIterator first, ForwardIterator last, const T& val);  
该算法等效于：  
template <class ForwardIterator, class T>  
void fill (ForwardIterator first, ForwardIterator last, const T& val)  
\{  
while (first != last) \{  
\*first = val;  
\++first;  
\}  
\}  
  
  
Example:  
int main ()  
\{  
vector<int> myvector (8);  // myvector: 0 0 0 0 0 0 0 0**  
   **fill (myvector.begin(),myvector.begin()+4,1);**  **// myvector: 1 1 1 1 0 0 0 0**   
 **fill (myvector.begin()+3,myvector.end()-2,2);  // myvector: 1 1 1 2 2 2 0 0**

**//myvector contains:**

**for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)  
 \{   
 cout << ' ' << \*it;// 1 1 1 2 2 2 0 0  
 \}**  
  
  **return 0;**   
**\}  
  
  
  
  
\*fill\_n**

**Assigns val to the first n elements of the sequence pointed by first.**

**原型：**

**template <class OutputIterator, class Size, class T>  
void fill\_n (OutputIterator first, Size n, const T& val);**  
 **该算法等效于：**   
 **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  
\}  
  
  
Example:  
 int main ()  
\{  
vector<int> myvector (8,1);  // myvector: 1 1 1 1 1 1 1 1  
 std::fill\_n (myvector.begin(),4,2);  // myvector: 2 2 2 2 1 1 1 1  
  
 //myvector contains:  
 for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)  
 \{   
 cout << ' ' << \*it;//2 2 2 2 1 1 1 1  
 \}  
  
 return 0;  
\}  
  
Tips:  
fill\_n假定对指定数量的元素做写操作时是安全的，所以要确保容器有足够的空间。  
  
  
  
  
\*replace  
Assigns new\_value to all the elements in the range \[first,last) that compare equal to old\_value.  
原型：  
template <class ForwardIterator, class T>  
void replace (ForwardIterator first, ForwardIterator last,  
const T& old\_value, const T& new\_value);  
该算法等效于：  
template <class ForwardIterator, class T>  
void replace (ForwardIterator first, ForwardIterator last,  
const T& old\_value, const T& new\_value)  
\{  
while (first!=last) \{  
if (\*first == old\_value) \*first=new\_value;  
\++first;  
\}  
\}  
  
  
Example:  
int main ()  
\{  
int myints\[\] = \{ 1,1,1,3,2,2,1,3 \};  
vector<int> myvector (myints, myints+8);  // 1,1,1,3,2,2,1,3**

**replace (myvector.begin(), myvector.end(), 3, 2);// 1,1,1,2,2,2,1,2**

**//myvector contains:  
 for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)  
 \{   
 cout << ' ' << \*it;// 1,1,1,2,2,2,1,2  
 \}  
  
 return 0;  
\}**