C++语法基础--泛型算法（generic algorithm)--replace_copy(),unique_copy,copy()

矫情吗；* 2022-01-10 04:09 168阅读 0赞

***注：泛型算法系列笔记是写给自己看的。所以做整理时保留了英文的解释。***

**1.replace\_copy**

**Copies the elements in the range \[first,last) to the range beginning at result, replacing the appearances of old\_value by new\_value.  
原型：  
template <class InputIterator, class OutputIterator, class T>  
OutputIterator replace\_copy (InputIterator first, InputIterator last,  
OutputIterator result,  
const T& old\_value, const T& new\_value);  
  
  
该算法等效于：  
template <class InputIterator, class OutputIterator, class T>  
OutputIterator replace\_copy (InputIterator first, InputIterator last,  
OutputIterator result, const T& old\_value, const T& new\_value)  
\{  
while (first!=last) \{  
\*result = (\*first==old\_value)? new\_value: \*first;  
\++first; ++result;  
\}  
return result;  
\}  
  
  
解析：  
first, last：Input iterators to the initial and final positions in a sequence.  
result：Output iterator to the initial position of the range where the resulting sequence is stored.  
old\_value：Value to be replaced.  
new\_value：Replacement value.  
Return：An iterator pointing to the element that follows the last element written in the result sequence.  
  
Example:  
int main ()  
\{  
int myints\[\] = \{ 10, 20, 30, 30, 20, 10, 10, 20 \};  
  
  
vector<int> myvector (8);  
replace\_copy (myints, myints+8, myvector.begin(), 20, 99);//把所有20换成99  
  
  
 // myvector contains:  
 for (int x:myvector)  
 \{   
std::cout << ' ' << x;//10 99 30 30 99 10 10 99  
 \}  
  
 return 0;  
\}  
  
  
  
  
  
  
2.unique\_copy  
Copies the elements in the range \[first,last) to the range beginning at result,  
except consecutive duplicates (elements that compare equal to the element preceding).  
原型：  
 equality ：  
template <class InputIterator, class OutputIterator>  
OutputIterator unique\_copy (InputIterator first, InputIterator last,  
OutputIterator result);  
predicate ：  
template <class InputIterator, class OutputIterator, class BinaryPredicate>  
OutputIterator unique\_copy (InputIterator first, InputIterator last,  
OutputIterator result, BinaryPredicate pred);  
  
解析：  
 first, last：Forward iterators to the initial and final positions in a sequence.  
result：Output iterator to the initial position of the range where the resulting range of values is stored.  
pred：Binary function that accepts two elements in the range as argument, and returns a value convertible to bool.  
return: An iterator pointing to the end of the copied range, which contains no consecutive duplicates.  
  
  
该算法等效于：  
template <class InputIterator, class OutputIterator>  
OutputIterator unique\_copy (InputIterator first, InputIterator last,  
OutputIterator result)  
\{  
if (first==last) return last;  
  
  
\*result = \*first;  
while (++first != last) \{  
typename iterator\_traits<InputIterator>::value\_type val = \*first;  
if (!(\*result == val)) // or: if (!pred(\*result,val)) for version (2)  
\*(++result)=val;  
\}  
return ++result;  
\}  
  
  
Example:  
  
  
int main()  
\{  
int arr\[\]=\{1,2,3,2,1,2\};  
vector<int> vec(arr,arr+6);  
vector<int> vec1;  
sort(vec.begin(),vec.end());  
unique\_copy(vec.begin(),vec.end(), back\_inserter(vec1),  
\[\](int a, int b)->int\{ return a==b; \}); //lambda表达式  \[\](int a, int b)->int\{ return a==b; \}  
for(int x:vec1)  //相当于 int (int a,intb)\{ return a==b;\}  
\{   
cout<<x<<'\\t';//1 2 3  
\}**

**\}**

**3.copy**

**Copies the elements in the range \[first,last) into the range beginning at result.  
原型：  
 template <class InputIterator, class OutputIterator>  
OutputIterator copy (InputIterator first, InputIterator last, OutputIterator result);  
  
该算法等效于：  
template<class InputIterator, class OutputIterator>  
OutputIterator copy (InputIterator first, InputIterator last, OutputIterator result)  
\{  
while (first!=last) \{  
\*result = \*first;  
\++result; ++first;  
\}  
return result;  
\}  
  
  
Example:  
 int main ()   
\{   
 int myints\[\]=\{1,2,3,4,5\};  
 vector<int> myvector (5);  
  
  
 copy ( myints, myints+5, myvector.begin() );  
 for(int x:myvector)  
 \{   
 cout<<x<<'\\t'; //1 2 3 4 5  
 \}  
  
 return 0;  
\}**