如何将向量转换为数组?

How do I convert a std::vector<double> to a double array[]?

如何将std::vector 转换为double array[]?

9 个解决方案

#1

There's a fairly simple trick to do so, since the spec now guarantees vectors store their elements contiguously:

这里有一个相当简单的技巧，因为规范现在保证向量连续地存储它们的元素:

std::vector<double> v;
double* a = &v[0];

#2

What for? You need to clarify: Do you need a pointer to the first element of an array, or an array?

对什么?您需要澄清:需要指向数组的第一个元素的指针还是数组的指针?

If you're calling an API function that expects the former, you can do do_something(&v[0], v.size()), where v is a vector of doubles. The elements of a vector are contiguous.

如果您正在调用一个期望使用前者的API函数，您可以使用do_something(&v[0]， v.size())，其中v是一个双精度向量。向量的元素是连续的。

Otherwise, you just have to copy each element:

否则，您只需复制每个元素:

double arr[100];
std::copy(v.begin(), v.end(), arr);

Ensure not only thar arr is big enough, but that arr gets filled up, or you have uninitialized values.

确保不仅thar arr足够大，而且arr被填满，或者您有未初始化的值。

#3

For C++11, vector.data() will do the trick.

对于c++ 11，使用vector.data()就可以了。

#4

vector<double> thevector;
//...
double *thearray = &thevector[0];

This is guaranteed to work by the standard, however there are some caveats: in particular take care to only use thearray while thevector is in scope.

这是标准的保证，但是有一些注意事项:特别要注意的是，在vector在范围内时，只使用thearray。

#5

Vectors effectively are arrays under the skin. If you have a function:

有效的向量是皮肤下的阵列。如果你有一个函数:

void f( double a[]);

you can call it like this:

你可以这样称呼它:

vector <double> v;
v.push_back( 1.23 )
f( &v[0] );

You should not ever need to convert a vector into an actual array instance.

您不应该需要将向量转换为实际的数组实例。

#6

If you have a function, then you probably need this:foo(&array[0], array.size());. If you managed to get into a situation where you need an array then you need to refactor, vectors are basically extended arrays, you should always use them.

如果您有一个函数，那么您可能需要这个:foo(&array[0]， array.size();如果你想要进入一个需要一个数组的情况，那么你需要重构，向量基本上是扩展数组，你应该经常使用它们。

#7

We can do this using data() method. C++11 provides this method.

我们可以使用data()方法来实现这一点。c++ 11提供这种方法。

Code Snippet

#include<bits/stdc++.h>
using namespace std;


int main()
{
  ios::sync_with_stdio(false);

  vector<int>v = {7, 8, 9, 10, 11};
  int *arr = v.data();

  for(int i=0; i<v.size(); i++)
  {
    cout<<arr[i]<<" ";
  }

  return 0;
}

#8

std::vector<double> vec;
double* arr = vec.data();

#9

You can do some what like this

你可以这样做

vector <int> id;
vector <double> v;

if(id.size() > 0)
{
    for(int i = 0; i < id.size(); i++)
    {
        for(int j = 0; j < id.size(); j++)
        {
            double x = v[i][j];
            cout << x << endl;
        }
    }
}