Both std::copy and std::fill are c++ algorithms of c++ STL. They can be used for c++ range and memory operations.

std::copy

As the name, std::copy copies data from one area to another area.

st::copy: Copy from one std::vector range to another std::vector range

The target range must be allocated bigger than or equal to the source range. And their value type must be the same.

#include <algorithm>
#include <iostream>
#include <vector>

int main()
{
	auto v1 = std::vector<int>{2, 3, 4, 7, 1, 5};
	auto v2 = std::vector<int>(v1.size());	// v2 is allocated the same size as v1 size.

	// std::copy: copy from v1 to v2
	std::copy(v1.begin(), v1.end(), v2.begin());

	for (const auto x: v2)
		std::cout << x << ' ';
	std::cout << std::endl;
}
/* output:
2 3 4 7 1 5
*/

(.begin(), .end(): Return c++ iterator, Read std::vector iterator) .

std::copy: Copy from memory to memory

#include <algorithm>
#include <iostream>

int main()
{
	int size = 7;
	int * mm1 = new int[size];

	// Initialize all values of mm1
	for (int i=0; i<size; ++i)
		mm1[i] = i * 2 + 3;

	int * mm2 = new int[size];	// allocate the same size as mm1 size.

	// Copy Memory !!
	// std::copy: copy from mm1 to mm2
	std::copy(mm1, mm1+size, mm2);

	// output
	for (int i=0; i<size; ++i)
		std::cout << mm2[i] << ' ';
	std::cout << std::endl;

	// delete
	delete [] mm1;	// delete an array created by new, use symbols: []
	delete [] mm2;
}
/* output:
3 5 7 9 11 13 15
*/

std::copy: Copy from raw memory to std::vector

Actually, std::vector object is memory too.

#include <algorithm>
#include <iostream>
#include <vector>

int main()
{
	int size = 11;
	int * mm = new int[size];
	for (int i=0; i<size; ++i)
		mm[i] = i*2;

	auto vv = std::vector<int>(size);	// allocate the same size

	// std::copy: copy from mm to vv
	std::copy(mm, mm+size, vv.begin());

	// output
	for (int i=0; i<vv.size(); ++i)
		std::cout << vv[i] << ' ';
	std::cout << std::endl;

	delete [] mm;
}

std::fill

As the name, std::fill fills an area with data.

std::fill: Fill std::vector

#include <algorithm>
#include <iostream>
#include <vector>

int main()
{
	auto v1 = std::vector<char>(7);	// Allocate std::vector object with size 7.

	// std::fill: fill all elements with 'G'
	std::fill(v1.begin(), v1.end(), 'G');

	// output
	for (const char x: v1)
		std::cout << x << ' ';
	std::cout << std::endl;
}
/* output:
G G G G G G G
*/

std::fill: Fill memory created by new

#include <algorithm>
#include <iostream>

int main()
{
	int size = 11;
	float * mm = new float[size];	// size: 11

	// std::fill: fill all element with 2.3
	std::fill(mm, mm+size, 2.3f);

	for (int i=0; i<size; ++i)
		std::cout << mm[i] << ' ';
	std::cout << std::endl;

	delete [] mm;	// delete
}
/* output:
2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3
*/

Written on Dec 09, 2024

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c++ std::exception:

std::cout.write(err.data(), err.size());

std::cout << std::endl;

caught:

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