📅 最后修改于: 2020-10-16 14:13:54 🧑 作者: Mango
C++ STL algorithm.replace_copy_if()函数用于将范围[first，last)复制到从结果开始的范围，并用new_value放置pred返回true的范围。它使用谓词pred代替运算符==来比较元素。
此函数检查源范围中的每个元素，如果将结果复制到新的目标范围中，则如果满足指定谓词，则将其替换。
template
OutputIterator replace_copy_if (InputIterator first, InputIterator last,
OutputIterator result, UnaryPredicate pred, const T& new_value);
first：一个输入迭代器，它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。
结果：一个输出迭代器，该迭代器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，则必须满足的一元谓词。
old_value：要替换的元素的旧值。
new_value：分配给具有旧值的元素的新值。
replace_copy_if()函数返回一个输出迭代器，该迭代器指向在结果序列中写入的最后一个元素的位置。
复杂度在第一个和最后一个之间是线性的：应用pred并为每个元素执行一个赋值。
访问范围为[first1，last1)的对象。
结果和返回值范围内的对象将被修改。
如果pred，元素分配或迭代器上的任何操作引发异常，则此函数引发异常。
请注意，无效的参数会导致未定义的行为。
让我们看一个简单的示例，以演示replace_copy_if()的用法：
#include
#include
#include
#include
using namespace std;
int main() {
vector v = { 3,1,2,1,2 };
replace_copy_if(v.begin(), v.end(),
ostream_iterator(cout, ","),
[](int x) { return x%2 != 0; }, 10);
return 0;
}
输出：
10,10,2,10,2,
让我们看另一个简单的例子：
// CPP code to illustrate
// replace_copy_if
#include
#include
#include
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& 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& v1, vector& v2)
{
replace_copy_if(v1.begin(), v1.end(), v2.begin(), IsEven, 0);
}
// Driver Code
int main()
{
vector 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
让我们看另一个简单的例子：
#include
#include
#include
#include
using namespace std;
int main()
{
const int MAX_ELEMENTS = 8 ;
// Define a template class vector of integers
typedef vector 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(), 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 }
让我们看另一个简单的例子：
#include
#include
#include
#include
bool greater6 ( int value ) {
return value >6;
}
int main( ) {
using namespace std;
vector v1;
list L1 (13);
vector ::iterator Iter1;
list ::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 ).