你如何删除c ++中的变量？

Question

How do you delete variables in a c++ program? i have a simple int list[10]; and i want delete it and change it to int list[9] . i would use vectors, but i still want to know how to do it

Answer 1

If you have something declared like this:

int list[10];

there is no way to "delete" it. It is either a global variable, with statically allocated storage, or it is a local variable with storage on the stack.

I don't know exactly what you are trying to accomplish, but maybe something like this will help you figure it out:

int *list = new int[10];  // allocate a new array of 10 ints
delete [] list;           // deallocate that array
list = new int[9];        // allocate new array with 9 ints

As you suggest in your question, you will almost always be better off using std::vector , std::list , and the like rather than using raw C-style arrays.

Answer 2

This is not called deleting a variable but instead redefining the type of a variable. This is simply not possible in C++. Once a variable type has been established it cannot be changed.

There are several ways to emulate or work around this behavior ...

• Create a child scope and define a new variable of the same name with a different type.
• Switch list to an int* and allocate it's memory on the heap. This will have the effect of redefining it to a different size without changing it's type.

Answer 3

If your array is allocated on the heap, then:

int *L = new int[10];
delete[] L;
L = new int[9];

There is no concept of "deleting" a local variable declared on the stack.

Answer 4

To delete an array in C++ you'd use the delete[] operator. See this link .

You'll want to be careful. What you have is a static array. When you use delete or delete[] it must be on dynamically allocated variables (ones you made with new ). To do that:

int* list = new int[10];
//...Code...
delete[] list;
list = new int[9];

Don't forget to delete if you new ! (Ideally you should use something managed so you can't forget, like you said).

Answer 5

Your int list[10]; is a static one. Arrays that are declared as variables are static objects in C++, and you can't delete/create them... it's a compile time thing.

You need to explicitly declare your array as an array object, say

int *list=new int[10];

Although it still seams a declaration, it's not: the new operand will trigger mem-allocation code)... If you want to allocate more or less space you need to free it first:

delete[] list;

and then use the new operand to make a new on (of the same int type)

Answer 6

Of course, you could always do this:

{
  int list[10];
  ... 'list' has 10 elements ...

  {
    int list[9];
    ... 'list' has 9 elements ... other 'list' inaccessible
  }
  ... 'list' 10 elements ... other 'list' non-existent.
}

Can't imagine why you would though.