C++ 如何将 std::array 的内容复制到另一个？

Question

关于如何将一个标准的 c 数组复制到另一个数组是众所周知的：

char test[20] = "asdasd";
char test2[19] = "asdassdsdfd";
strcpy_s(test, sizeof(test), test2);

但是我怎样才能对 std::array 做同样的事情呢？（最好没有 for 循环）

std::array<char, 20> test = {"asdasd"};
std::array<char, 19> test2 = {"asdassdsdfd"};
// copy test2 into test

Answer 1

这是对您正在尝试做的事情的更详尽的回答。不过，我真的不建议使用数组来保存字符串。

#include <array>
#include <iostream>

// copy solution without loops, though probably it would have been more readable with them :)
template<typename type_t, std::size_t N1, std::size_t N2>
void copy_array(const std::array<type_t, N1>& source, std::array<type_t, N2>& destination)
{
    // copy to a larger destination 
    if constexpr (N1 <= N2)
    {
        // this will copy the whole array! not just the characters from the string literal!
        std::copy(source.begin(), source.end(), destination.begin());

        // fill remainder of destination with 0's
        auto it = destination.begin();
        std::advance(it, N1);
        std::fill(it, destination.end(), 0);
    }
    else
    // copy into a smaller array, then copy only the beginning
    // note this will also result in an array without trailing 0's
    // an array is NOT a string.
    {
        
        auto end = source.begin();
        std::advance(end, N2);
        std::copy(source.begin(), end, destination.begin());
    }
}

int main()
{
    // Note you're probably better of just using const std::strings instead of std::arrays
    // this also avoids the pain involved in copying rules for mismatching array sizes.
    // The arrays initialized with string literals smaller then their size initialize the 
    // rest of the array to 0's
    std::array<char, 20> test{ "asdasd" };
    std::array<char, 19> test2{ "asdassdsdfd" };

    copy_array(test2, test);
    
    for (const auto c : test)
    {
        std::cout << c;
    }
}

Answer 2

方法有很多种。您可以使用 strcpy_s(test.data(), sizeof(test), test2.data())，但我不推荐它。基本相同的更通用版本是 std::copy_n(test.begin(), test.size(), test2.begin());，即使 std::array 中的类型发生变化，它也将继续正确。鉴于它们的大小是静态的，我会投入 static_assert(test.size() <= test2.size()); 以备不时之需。

Answer 3

我可以提供使用算法深度优先搜索。毫无疑问，它是不合理的，但它执行了当前问题中描述的要求。

#include <iostream>
#include <array>
#include <vector>
using namespace std;
const int maximumSize=20;
//copy test2 into test
array<char, 20> test = {"asdasd"};
array<char, 19> test2 = {"asdassdsdfd"};
vector<int> visited(maximumSize, 0);
template<typename Type>
void showContent1D(Type input)
{
    for(int i=0; i<input.size(); ++i)
    {
        cout<<input[i]<<", ";
    }
    return;
}
void depthFirstSearch(int firstIndex)
{
    if(visited[firstIndex]==1)
    {
        return;
    }
    visited[firstIndex]=1;
    test[firstIndex]=test2[firstIndex];
    for(int index=0; index<test2.size(); ++index)
    {
        depthFirstSearch(index);
    }
    return;
}
int main()
{
    cout<<"Before copying:"<<endl<<"test <- ";
    showContent1D(test);
    cout<<endl<<"test2 <- ";
    showContent1D(test2);
    cout<<endl<<"<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<"<<endl;
    depthFirstSearch(0);
    cout<<"After copying:"<<endl<<"test <- ";
    showContent1D(test);
    cout<<endl<<"test2 <- ";
    showContent1D(test2);
    return 0;
}

输出在这里：

Before copying:
test <- a, s, d, a, s, d, , , , , , , , , , , , , , , 
test2 <- a, s, d, a, s, s, d, s, d, f, d, , , , , , , , , 
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
After copying:
test <- a, s, d, a, s, s, d, s, d, f, d, , , , , , , , , , 
test2 <- a, s, d, a, s, s, d, s, d, f, d, , , , , , , , ,

C++ 如何将 std::array 的内容复制到另一个？

C++ how to copy contents of std::array to another?

c++

arrays

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