C++ replace_copy_if()
C++ 算法replace_copy_if()
C++ 算法 replace_copy_if()函数用于将范围[first，last)复制到该范围从结果开始，按new_value放置 pred 对于其返回true的那些。它使用谓词 pred 而不是operator ==来比较元素。
此函数检查源范围中的每个元素，并在复制结果时满足指定谓词的情况下将其替换。进入新的目标范围。
语法
template <class InputIterator, class OutputIterator, class UnaryPredicate, class T>
OutputIterator replace_copy_if (InputIterator first, InputIterator last,
OutputIterator result, UnaryPredicate pred, const T& new_value);
参数
first: 一个输入迭代器，指向要替换元素的范围内的初始位置。
last: 一个输入迭代器，它指向要替换元素的范围内的最终位置。
result: 一个输出迭代器，它指向存储结果序列的范围的第一个元素。
pred : 如果要替换元素的值，则必须满足一元谓词。
new_value : 分配给具有旧值的元素的新值。
返回值
replace_copy_if()函数返回一个输出迭代器，该迭代器指向指向结果序列中最后写入的元素的位置。
复杂度
首尾之间的距离是线性的: 应用pred并为每个元素执行赋值。
数据竞争
访问范围为[first1，last1)的对象。
结果范围内的对象和返回的值将被修改。
异常安全
如果pred，元素分配或迭代器上的任何操作引发异常，则此函数将引发异常。
请注意，无效参数会导致未定义的行为。
示例1
让我们看一个简单的示例来演示replace_copy_if()的用法:
#include <algorithm>
#include <iostream>
#include <vector>
#include <iterator>
using namespace std;
int main() {
vector<int> v = { 3,1,2,1,2 };
replace_copy_if(v.begin(), v.end(),
ostream_iterator<int>(cout, ","),
[](int x) { return x%2 != 0; }, 10);
return 0;
}
输出:
示例2
让我们看另一个简单的示例:
// CPP code to illustrate
// replace_copy_if
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
// Function to check if number is even
int IsEven(int i)
{
return ((i % 2) == 0);
}
// Function to print content of vector
void print(vector<int>& v)
{
int len = v.size();
for (int i=0; i < len; i++)
cout << v[i] << " ";
cout << endl;
}
// Function to replace all even numbers from vector v1 and
// copying them to v2
void replace_copy_ifDemo(vector<int>& v1, vector<int>& v2)
{
replace_copy_if(v1.begin(), v1.end(), v2.begin(), IsEven, 0);
}
// Driver Code
int main()
{
vector<int> v1, v2;
for (int i = 1; i <= 10; i++)
v1.push_back(i);
cout << "Before replace_copy_if: ";
print(v1);
v2.resize(v1.size()); // allocate space
replace_copy_ifDemo(v1, v2);
cout << "After replace_copy_if: ";
print(v2);
return 0;
}
输出:
Before replace_copy_if: 1 2 3 4 5 6 7 8 9 10
After replace_copy_if: 1 0 3 0 5 0 7 0 9 0
示例3
让我们看另一个简单的示例:
#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
using namespace std;
int main()
{
const int MAX_ELEMENTS = 8 ;
// Define a template class vector of integers
typedef vector<int > IntVector ;
//Define an iterator for template class vector of integer
typedef IntVector::iterator IntVectorIt ;
//vector containing numbers
IntVector Numbers(MAX_ELEMENTS), Result(MAX_ELEMENTS) ;
IntVectorIt start, end, it, last, resultIt ;
//Initialize vector Numbers
Numbers[0] = 10 ;
Numbers[1] = 20 ;
Numbers[2] = 10 ;
Numbers[3] = 15 ;
Numbers[4] = 12 ;
Numbers[5] = 7 ;
Numbers[6] = 9 ;
Numbers[7] = 10 ;
start = Numbers.begin() ; // location of first
// element of Numbers
end = Numbers.end() ; // one past the location
// last element of Numbers
resultIt = Result.begin() ; // location of first
// element of Result
// print content of Numbers
cout << "Numbers { " ;
for(it = start; it != end; it++)
cout << *it << " " ;
cout << " }\n" << endl ;
// copy all elements from Numbers to Result
// replacing any item that >= 10 with 30
last = replace_copy_if(start, end, resultIt,
bind2nd(greater_equal<int>(), 10), 30) ;
//print number of elements copied to Result
cout << "Total number of elements copied to Result = "
<< last-resultIt << endl ;
start = Result.begin() ; // location of first
// element of Result
end = Result.end() ; // one past the location
// last element of Result
// print content of Result
cout << "Result { " ;
for(it = start; it != end; it++)
cout << *it << " " ;
cout << " }\n" << endl ;
}
输出:
Numbers { 10 20 10 15 12 7 9 10 }
Total number of elements copied to Result = 8
Result { 30 30 30 30 30 7 9 30 }
示例4
让我们看另一个简单的示例:
#include <vector>
#include <list>
#include <algorithm>
#include <iostream>
bool greater6 ( int value ) {
return value >6;
}
int main( ) {
using namespace std;
vector <int> v1;
list <int> L1 (13);
vector <int>::iterator Iter1;
list <int>::iterator L_Iter1;
int i;
for ( i = 0 ; i <= 9 ; i++ )
v1.push_back( i );
int ii;
for ( ii = 0 ; ii <= 3 ; ii++ )
v1.push_back( 7 );
random_shuffle ( v1.begin( ), v1.end( ) );
int iii;
for ( iii = 0 ; iii <= 13 ; iii++ )
v1.push_back( 1 );
cout << "The original vector v1 is:\n ( " ;
for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
cout << *Iter1 << " ";
cout << ")." << endl;
// Replace elements with a value of 7 in the 1st half of a vector
// with a value of 70 and copy it into the 2nd half of the vector
replace_copy_if ( v1.begin( ), v1.begin( ) + 14,v1.end( )-14,
greater6 , 70);
cout << "The vector v1 with values of 70 replacing those greater"
<< "\n than 6 in the 1st half & copied into the 2nd half is:\n ( " ;
for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
cout << *Iter1 << " ";
cout << ")." << endl;
// Replace elements in a vector with a value of 70
// with a value of 1 and copy into a list
replace_copy_if ( v1.begin( ), v1.begin( ) + 13,L1.begin( ),
greater6 ,-1 );
cout << "A list copy of vector v1 with the value-1\n replacing "
<< "those greater than 6 is:\n ( " ;
for ( L_Iter1 = L1.begin( ) ; L_Iter1 != L1.end( ) ; L_Iter1++ )
cout << *L_Iter1 << " ";
cout << ")." << endl;
}
输出:
The original vector v1 is:
( 4 7 7 7 0 5 7 1 6 9 3 7 8 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ).
The vector v1 with values of 70 replacing those greater
than 6 in the 1st half & copied into the 2nd half is:
( 4 7 7 7 0 5 7 1 6 9 3 7 8 2 4 70 70 70 0 5 70 1 6 70 3 70 70 2 ).
A list copy of vector v1 with the value-1
replacing those greater than 6 is:
( 4-1-1-1 0 5-1 1 6-1 3-1-1 ).
