stl中copy()函数

C ++ STL std :: copy_if()函数 (C++ STL std::copy_if() function)

copy_if() function is a library function of algorithm header, it is used to copy the elements of a container, it copies the certain elements (which satisfy the given condition) of a container from the given start position to another container from the given beginning position.

copy_if()函数是算法标头的库函数，用于复制容器的元素，它将容器的某些元素(满足给定条件)从给定的开始位置复制到另一个容器，从给定的开始位置位置。

Note:To use copy_if() function – include <algorithm> header or you can simple use <bits/stdc++.h> header file.

注意：要使用copy_if()函数 –包括<algorithm>头文件，或者您可以简单地使用<bits / stdc ++。h>头文件。

Syntax of std::copy_if() function

std :: copy_if()函数的语法

    std::copy_n(
iterator source_first,
iterator source_end,
iterator target_start,
UnaryPredicate pred);

Parameter(s):

参数：

• iterator source_first, iterator source_end – are the iterator positions of the source container.

  迭代器source_first，迭代器source_end –是源容器的迭代器位置。

• iterator target_start – is the beginning iterator of the target container.

  迭代器target_start –是目标容器的开始迭代器。

• UnaryPredicate pred – Unary function which accepts an element in the range as an argument, and returns a value convertible to bool.

  UnaryPredicate pred –一元函数，该函数接受范围内的元素作为参数，并返回可转换为bool的值。

Return value: iterator – it is an iterator to the end of the target range where elements have been copied.

返回值： 迭代器 –它是目标元素已复制到目标范围末尾的迭代器。

Example:

例：

    Input:
//declaring & initializing an int array
int arr[] = { 10, 20, 30, 40, 50 };
//vector declaration
vector<int> v1(5);
//copying 5 array elements to the vector
copy_n(arr, 5, v1.begin());
Output:
//if we print the value
arr: 10 20 30 40 50
v1: 10 20 30 40 50

C ++ STL程序演示std :: copy_if()函数的使用 (C++ STL program to demonstrate use of std::copy_if() function)

In this example, we are copying only positive elements of the array to the vector.

在此示例中，我们仅将数组的正元素复制到向量。

//C++ STL program to demonstrate use of
//std::copy_if() function
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main()
{//declaring & initializing an int array
int arr[] = { 10, 20, 30, -10, -20, 40, 50 };
//vector declaration
vector<int> v1(7);
//copying 5 array elements to the vector
copy_if(arr, arr + 7, v1.begin(), [](int i) { return (i >= 0); });
//printing array
cout << "arr: ";
for (int x : arr)
cout << x << " ";
cout << endl;
//printing vector
cout << "v1: ";
for (int x : v1)
cout << x << " ";
cout << endl;
return 0;
}

Output

输出量

arr: 10 20 30 -10 -20 40 50
v1: 10 20 30 40 50 0 0

Reference: C++ std::copy_if()

参考： C ++ std :: copy_if()

翻译自: https://www.includehelp.com/stl/std-copy_if-function-with-example.aspx

stl中copy()函数