c++ - 静态与动态数组 C++

Question

C++ 编译器的行为可能不同。由于 C++ 中的数组可以使用以下方法声明:

方法一:

int size;
cout << "Enter size of array: ";
cin >> size;

int x[size];  
for (int i = 0; i < size; i++)
{
    //cout << "x[" << i << "] = ";
    x[i] = i + 1;
}  

方法B

int size;
cout << "Enter size of array: ";
cin >> size;

int *x = new int[size];  
for (int i = 0; i < size; i++)
{
    //cout << "x[" << i << "] = ";
    x[i] = i + 1;
}

通过在运行时 获取用户的输入，两者都可以正常工作。我知道，使用方法 B，我们必须像 delete [] x 一样删除 x。

• 为什么要使用 int *x = new int[size];，如果两者服务相同目的？
• 使用 new 有什么好处？

以下是我正在测试的代码片段:

#include<iostream>
using namespace std;

int main()
{
    int size;
    cout << "Enter size of array: ";
    cin >> size;

    //int *x = new int[size];
    int x[size];

    for (int i = 0; i < size; i++)
    {
        //cout << "x[" << i << "] = ";
        x[i] = i + 1;
    }

    cout << endl << "Display" << endl;
    for (int i = 0; i < size; i++)
    {
        cout << "x[" << i << "] = " << x[i] << endl;
    }  
    return 0;  
}

Answer 1

C++ 标准没有定义方法 A，但在 ISO C99 中是允许的，GCC 在 C++ 模式下也支持它。来自 https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html :

Variable-length automatic arrays are allowed in ISO C99, and as an extension GCC accepts them in C90 mode and in C++. These arrays are declared like any other automatic arrays, but with a length that is not a constant expression. The storage is allocated at the point of declaration and deallocated when the block scope containing the declaration exits.

我刚刚在这里找到了一些相关的讨论:Variable Length Arrays in C++14?